MM-8607 Add ability to turn off non-critical services when under load (#13212)

* MM-8607: add ability to turn off non-critical services under load

* server busy invalid param unit tests

* MM-8607: rename server busy endpoints

* MM-8607: handle case where App not initialized

* MM-8607: additional unit test cases per feedback.

* MM-8607: use decorator to check isbusy when adding endpoint route

* MM-8607: rename endpoints, use struct for json

* Update api4/system.go

Fix misspelled log output

Co-Authored-By: Saturnino Abril <saturnino.abril@gmail.com>

* MM-8607: fix i18n order; max seconds for server busy expiry

api4/user.go

@@ -24,7 +24,7 @@ func (api *API) InitUser() {
 	api.BaseRoutes.Users.Handle("", api.ApiSessionRequired(getUsers)).Methods("GET")
 	api.BaseRoutes.Users.Handle("/ids", api.ApiSessionRequired(getUsersByIds)).Methods("POST")
 	api.BaseRoutes.Users.Handle("/usernames", api.ApiSessionRequired(getUsersByNames)).Methods("POST")
-	api.BaseRoutes.Users.Handle("/search", api.ApiSessionRequired(searchUsers)).Methods("POST")
+	api.BaseRoutes.Users.Handle("/search", api.ApiSessionRequiredDisableWhenBusy(searchUsers)).Methods("POST")
 	api.BaseRoutes.Users.Handle("/autocomplete", api.ApiSessionRequired(autocompleteUsers)).Methods("GET")
 	api.BaseRoutes.Users.Handle("/stats", api.ApiSessionRequired(getTotalUsersStats)).Methods("GET")
 	api.BaseRoutes.Users.Handle("/group_channels", api.ApiSessionRequired(getUsersByGroupChannelIds)).Methods("POST")