Revert "app/pluginservice: move plugin out from the Channels product (#21697)" (#21725)

This reverts commit 6c55c4d356.

cmd/mattermost/commands/init.go

@@ -7,6 +7,7 @@ import (
 	"github.com/spf13/cobra"
 
 	"github.com/mattermost/mattermost-server/v6/app"
+	"github.com/mattermost/mattermost-server/v6/app/request"
 	"github.com/mattermost/mattermost-server/v6/config"
 	"github.com/mattermost/mattermost-server/v6/model"
 	"github.com/mattermost/mattermost-server/v6/shared/i18n"
@@ -20,7 +21,7 @@ func initDBCommandContextCobra(command *cobra.Command, readOnlyConfigStore bool)
 		panic(err)
 	}
 
-	a.Srv().InitializePluginService()
+	a.InitPlugins(request.EmptyContext(a.Log()), *a.Config().PluginSettings.Directory, *a.Config().PluginSettings.ClientDirectory)
 	a.DoAppMigrations()
 
 	return a, nil