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

app/server.go

@@ -53,6 +53,7 @@ type Server struct {
 	Server      *http.Server
 	ListenAddr  *net.TCPAddr
 	RateLimiter *RateLimiter
+	Busy        *Busy
 
 	didFinishListen chan struct{}
 
@@ -473,6 +474,7 @@ func (s *Server) Start() error {
 		s.RateLimiter = rateLimiter
 		handler = rateLimiter.RateLimitHandler(handler)
 	}
+	s.Busy = &Busy{}
 
 	// Creating a logger for logging errors from http.Server at error level
 	errStdLog, err := s.Log.StdLogAt(mlog.LevelError, mlog.String("source", "httpserver"))