MM-40813: Add config interface (#19571)

We create the basic boilerplate to pass services
to each product. The basic idea is to have a map
containing service names and the services.

The server will pass all services to all products.
But it is on the product, to choose what services
they will actually consume.

Each product will cast the received service to
an interface with the methods that product requires.

https://mattermost.atlassian.net/browse/MM-40813

```release-note
NONE
```

app/plugin.go

@@ -43,7 +43,7 @@ type pluginSignaturePath struct {
 // To get the plugins environment when the plugins are disabled, manually acquire the plugins
 // lock instead.
 func (ch *Channels) GetPluginsEnvironment() *plugin.Environment {
-	if !*ch.srv.Config().PluginSettings.Enable {
+	if !*ch.cfgSvc.Config().PluginSettings.Enable {
 		return nil
 	}
 
@@ -79,7 +79,7 @@ func (ch *Channels) syncPluginsActiveState() {
 		return
 	}
 
-	config := ch.srv.Config().PluginSettings
+	config := ch.cfgSvc.Config().PluginSettings
 
 	if *config.Enable {
 		availablePlugins, err := pluginsEnvironment.Available()
@@ -100,7 +100,7 @@ func (ch *Channels) syncPluginsActiveState() {
 
 			// Tie Apps proxy disabled status to the feature flag.
 			if pluginID == "com.mattermost.apps" {
-				if !ch.srv.Config().FeatureFlags.AppsEnabled {
+				if !ch.cfgSvc.Config().FeatureFlags.AppsEnabled {
 					pluginEnabled = false
 				}
 			}
@@ -174,10 +174,10 @@ func (ch *Channels) initPlugins(c *request.Context, pluginDir, webappPluginDir s
 	ch.pluginsLock.RLock()
 	pluginsEnvironment := ch.pluginsEnvironment
 	ch.pluginsLock.RUnlock()
-	if pluginsEnvironment != nil || !*ch.srv.Config().PluginSettings.Enable {
+	if pluginsEnvironment != nil || !*ch.cfgSvc.Config().PluginSettings.Enable {
 		ch.syncPluginsActiveState()
 		if pluginsEnvironment != nil {
-			pluginsEnvironment.TogglePluginHealthCheckJob(*ch.srv.Config().PluginSettings.EnableHealthCheck)
+			pluginsEnvironment.TogglePluginHealthCheckJob(*ch.cfgSvc.Config().PluginSettings.EnableHealthCheck)
 		}
 		return
 	}
@@ -207,7 +207,7 @@ func (ch *Channels) initPlugins(c *request.Context, pluginDir, webappPluginDir s
 	ch.pluginsEnvironment = env
 	ch.pluginsLock.Unlock()
 
-	ch.pluginsEnvironment.TogglePluginHealthCheckJob(*ch.srv.Config().PluginSettings.EnableHealthCheck)
+	ch.pluginsEnvironment.TogglePluginHealthCheckJob(*ch.cfgSvc.Config().PluginSettings.EnableHealthCheck)
 
 	if err := ch.syncPlugins(); err != nil {
 		mlog.Error("Failed to sync plugins from the file store", mlog.Err(err))
@@ -274,7 +274,7 @@ func (ch *Channels) syncPlugins() *model.AppError {
 		go func(pluginID string) {
 			defer wg.Done()
 			// Only handle managed plugins with .filestore flag file.
-			_, err := os.Stat(filepath.Join(*ch.srv.Config().PluginSettings.Directory, pluginID, managedPluginFileName))
+			_, err := os.Stat(filepath.Join(*ch.cfgSvc.Config().PluginSettings.Directory, pluginID, managedPluginFileName))
 			if os.IsNotExist(err) {
 				mlog.Warn("Skipping sync for unmanaged plugin", mlog.String("plugin_id", pluginID))
 			} else if err != nil {
@@ -307,7 +307,7 @@ func (ch *Channels) syncPlugins() *model.AppError {
 			defer reader.Close()
 
 			var signature filestore.ReadCloseSeeker
-			if *ch.srv.Config().PluginSettings.RequirePluginSignature {
+			if *ch.cfgSvc.Config().PluginSettings.RequirePluginSignature {
 				signature, appErr = ch.srv.fileReader(plugin.signaturePath)
 				if appErr != nil {
 					mlog.Error("Failed to open plugin signature from file store.", mlog.Err(appErr))
@@ -401,12 +401,12 @@ func (ch *Channels) enablePlugin(id string) *model.AppError {
 		return model.NewAppError("EnablePlugin", "app.plugin.not_installed.app_error", nil, "", http.StatusNotFound)
 	}
 
-	ch.srv.UpdateConfig(func(cfg *model.Config) {
+	ch.cfgSvc.UpdateConfig(func(cfg *model.Config) {
 		cfg.PluginSettings.PluginStates[id] = &model.PluginState{Enable: true}
 	})
 
 	// This call will implicitly invoke SyncPluginsActiveState which will activate enabled plugins.
-	if _, _, err := ch.srv.SaveConfig(ch.srv.Config(), true); err != nil {
+	if _, _, err := ch.cfgSvc.SaveConfig(ch.cfgSvc.Config(), true); err != nil {
 		if err.Id == "ent.cluster.save_config.error" {
 			return model.NewAppError("EnablePlugin", "app.plugin.cluster.save_config.app_error", nil, "", http.StatusInternalServerError)
 		}
@@ -447,13 +447,13 @@ func (ch *Channels) disablePlugin(id string) *model.AppError {
 		return model.NewAppError("DisablePlugin", "app.plugin.not_installed.app_error", nil, "", http.StatusNotFound)
 	}
 
-	ch.srv.UpdateConfig(func(cfg *model.Config) {
+	ch.cfgSvc.UpdateConfig(func(cfg *model.Config) {
 		cfg.PluginSettings.PluginStates[id] = &model.PluginState{Enable: false}
 	})
 	ch.unregisterPluginCommands(id)
 
 	// This call will implicitly invoke SyncPluginsActiveState which will deactivate disabled plugins.
-	if _, _, err := ch.srv.SaveConfig(ch.srv.Config(), true); err != nil {
+	if _, _, err := ch.cfgSvc.SaveConfig(ch.cfgSvc.Config(), true); err != nil {
 		return model.NewAppError("DisablePlugin", "app.plugin.config.app_error", nil, err.Error(), http.StatusInternalServerError)
 	}
 
@@ -561,7 +561,7 @@ func (ch *Channels) getPrepackagedPlugin(pluginID, version string) (*plugin.Prep
 // If version is empty, the latest compatible version is used.
 func (ch *Channels) getRemoteMarketplacePlugin(pluginID, version string) (*model.BaseMarketplacePlugin, *model.AppError) {
 	marketplaceClient, err := marketplace.NewClient(
-		*ch.srv.Config().PluginSettings.MarketplaceURL,
+		*ch.cfgSvc.Config().PluginSettings.MarketplaceURL,
 		ch.srv.HTTPService(),
 	)
 	if err != nil {
@@ -835,8 +835,8 @@ func (ch *Channels) getPluginsFromFilePaths(fileStorePaths []string) map[string]
 	pluginSignaturePathMap := make(map[string]*pluginSignaturePath)
 
 	fsPrefix := ""
-	if *ch.srv.Config().FileSettings.DriverName == model.ImageDriverS3 {
-		ptr := ch.srv.Config().FileSettings.AmazonS3PathPrefix
+	if *ch.cfgSvc.Config().FileSettings.DriverName == model.ImageDriverS3 {
+		ptr := ch.cfgSvc.Config().FileSettings.AmazonS3PathPrefix
 		if ptr != nil && *ptr != "" {
 			fsPrefix = *ptr + "/"
 		}
@@ -936,12 +936,12 @@ func (ch *Channels) processPrepackagedPlugin(pluginPath *pluginSignaturePath) (*
 	}
 
 	// Skip installing the plugin at all if automatic prepackaged plugins is disabled
-	if !*ch.srv.Config().PluginSettings.AutomaticPrepackagedPlugins {
+	if !*ch.cfgSvc.Config().PluginSettings.AutomaticPrepackagedPlugins {
 		return plugin, nil
 	}
 
 	// Skip installing if the plugin is has not been previously enabled.
-	pluginState := ch.srv.Config().PluginSettings.PluginStates[plugin.Manifest.Id]
+	pluginState := ch.cfgSvc.Config().PluginSettings.PluginStates[plugin.Manifest.Id]
 	if pluginState == nil || !pluginState.Enable {
 		return plugin, nil
 	}
@@ -956,16 +956,16 @@ func (ch *Channels) processPrepackagedPlugin(pluginPath *pluginSignaturePath) (*
 
 // installFeatureFlagPlugins handles the automatic installation/upgrade of plugins from feature flags
 func (ch *Channels) installFeatureFlagPlugins() {
-	ffControledPlugins := ch.srv.Config().FeatureFlags.Plugins()
+	ffControledPlugins := ch.cfgSvc.Config().FeatureFlags.Plugins()
 
 	// Respect the automatic prepackaged disable setting
-	if !*ch.srv.Config().PluginSettings.AutomaticPrepackagedPlugins {
+	if !*ch.cfgSvc.Config().PluginSettings.AutomaticPrepackagedPlugins {
 		return
 	}
 
 	for pluginID, version := range ffControledPlugins {
 		// Skip installing if the plugin has been previously disabled.
-		pluginState := ch.srv.Config().PluginSettings.PluginStates[pluginID]
+		pluginState := ch.cfgSvc.Config().PluginSettings.PluginStates[pluginID]
 		if pluginState != nil && !pluginState.Enable {
 			ch.srv.Log.Debug("Not auto installing/upgrade because plugin was disabled", mlog.String("plugin_id", pluginID), mlog.String("version", version))
 			continue