MM-12849 Moving all non request scoped items to Server struct (#9806)

* Moving goroutine pool

* Auto refactor

* Moving plugins.

* Auto refactor

* Moving fields to server

* Auto refactor

* Removing siteurl duplication.

* Moving reset of app fields

* Auto refactor

* Formatting

* Moving niling of Server to after last use

* Fixing unit tests.

app/plugin_statuses.go

@@ -11,11 +11,11 @@ import (
 
 // GetPluginStatuses returns the status for plugins installed on this server.
 func (a *App) GetPluginStatuses() (model.PluginStatuses, *model.AppError) {
-	if a.Plugins == nil || !*a.Config().PluginSettings.Enable {
+	if a.Srv.Plugins == nil || !*a.Config().PluginSettings.Enable {
 		return nil, model.NewAppError("GetPluginStatuses", "app.plugin.disabled.app_error", nil, "", http.StatusNotImplemented)
 	}
 
-	pluginStatuses, err := a.Plugins.Statuses()
+	pluginStatuses, err := a.Srv.Plugins.Statuses()
 	if err != nil {
 		return nil, model.NewAppError("GetPluginStatuses", "app.plugin.get_statuses.app_error", nil, err.Error(), http.StatusInternalServerError)
 	}