[MM-28630] Add ping endpoint to local mode (#15694)

api4/api.go

@@ -318,6 +318,7 @@ func InitLocal(configservice configservice.ConfigService, globalOptionsFunc app.
 	api.BaseRoutes.Groups = api.BaseRoutes.ApiRoot.PathPrefix("/groups").Subrouter()
 
 	api.BaseRoutes.LDAP = api.BaseRoutes.ApiRoot.PathPrefix("/ldap").Subrouter()
+	api.BaseRoutes.System = api.BaseRoutes.ApiRoot.PathPrefix("/system").Subrouter()
 	api.BaseRoutes.Posts = api.BaseRoutes.ApiRoot.PathPrefix("/posts").Subrouter()
 	api.BaseRoutes.Post = api.BaseRoutes.Posts.PathPrefix("/{post_id:[A-Za-z0-9]+}").Subrouter()
 	api.BaseRoutes.PostsForChannel = api.BaseRoutes.Channel.PathPrefix("/posts").Subrouter()