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/server.go

@@ -86,6 +86,12 @@ import (
 // declaring this as var to allow overriding in tests
 var SentryDSN = "placeholder_sentry_dsn"
 
+type ServiceKey string
+
+const (
+	ConfigKey ServiceKey = "config"
+)
+
 type Server struct {
 	sqlStore        *sqlstore.SqlStore
 	Store           store.Store
@@ -150,7 +156,7 @@ type Server struct {
 	searchConfigListenerId  string
 	searchLicenseListenerId string
 	loggerLicenseListenerId string
-	configStore             *config.Store
+	configStore             *configWrapper
 
 	telemetryService *telemetry.TelemetryService
 	userService      *users.UserService
@@ -231,7 +237,7 @@ func NewServer(options ...Option) (*Server, error) {
 			return nil, errors.Wrap(err, "failed to load config")
 		}
 
-		s.configStore = configStore
+		s.configStore = &configWrapper{srv: s, Store: configStore}
 	}
 
 	// Step 2: Logging
@@ -250,10 +256,13 @@ func NewServer(options ...Option) (*Server, error) {
 
 	s.httpService = httpservice.MakeHTTPService(s)
 
+	serviceMap := map[ServiceKey]interface{}{
+		ConfigKey: s.configStore,
+	}
 	// Step 3: Initialize products.
 	// Depends on s.httpService.
 	for name, initializer := range products {
-		prod, err2 := initializer(s)
+		prod, err2 := initializer(s, serviceMap)
 		if err2 != nil {
 			return nil, errors.Wrapf(err2, "error initializing product: %s", name)
 		}
@@ -755,7 +764,7 @@ func (s *Server) initLogging() error {
 		s.NotificationsLog = l.With(mlog.String("logSource", "notifications"))
 	}
 
-	if err := s.configureLogger("logging", s.Log, &s.Config().LogSettings, s.configStore, config.GetLogFileLocation); err != nil {
+	if err := s.configureLogger("logging", s.Log, &s.Config().LogSettings, s.configStore.Store, config.GetLogFileLocation); err != nil {
 		// if the config is locked then a unit test has already configured and locked the logger; not an error.
 		if !errors.Is(err, mlog.ErrConfigurationLock) {
 			// revert to default logger if the config is invalid
@@ -771,7 +780,7 @@ func (s *Server) initLogging() error {
 	mlog.InitGlobalLogger(s.Log)
 
 	notificationLogSettings := config.GetLogSettingsFromNotificationsLogSettings(&s.Config().NotificationLogSettings)
-	if err := s.configureLogger("notification logging", s.NotificationsLog, notificationLogSettings, s.configStore, config.GetNotificationsLogFileLocation); err != nil {
+	if err := s.configureLogger("notification logging", s.NotificationsLog, notificationLogSettings, s.configStore.Store, config.GetNotificationsLogFileLocation); err != nil {
 		if !errors.Is(err, mlog.ErrConfigurationLock) {
 			mlog.Error("Error configuring notification logger", mlog.Err(err))
 			return err