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/post.go

@@ -25,7 +25,7 @@ func (api *API) InitPost() {
 
 	api.BaseRoutes.ChannelForUser.Handle("/posts/unread", api.ApiSessionRequired(getPostsForChannelAroundLastUnread)).Methods("GET")
 
-	api.BaseRoutes.Team.Handle("/posts/search", api.ApiSessionRequired(searchPosts)).Methods("POST")
+	api.BaseRoutes.Team.Handle("/posts/search", api.ApiSessionRequiredDisableWhenBusy(searchPosts)).Methods("POST")
 	api.BaseRoutes.Post.Handle("", api.ApiSessionRequired(updatePost)).Methods("PUT")
 	api.BaseRoutes.Post.Handle("/patch", api.ApiSessionRequired(patchPost)).Methods("PUT")
 	api.BaseRoutes.PostForUser.Handle("/set_unread", api.ApiSessionRequired(setPostUnread)).Methods("POST")