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

web/handlers.go

@@ -66,6 +66,7 @@ type Handler struct {
 	TrustRequester      bool
 	RequireMfa          bool
 	IsStatic            bool
+	DisableWhenBusy     bool
 
 	cspShaDirective string
 }
@@ -159,6 +160,10 @@ func (h Handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 		c.MfaRequired()
 	}
 
+	if c.Err == nil && h.DisableWhenBusy && c.App.Srv.Busy.IsBusy() {
+		c.SetServerBusyError()
+	}
+
 	if c.Err == nil {
 		h.HandleFunc(c, w, r)
 	}