MM-10417 Improve HTTPService for use in image proxy (#9966)

* Replaced httpservice with proper http.Client

* Added HTTPService.MakeTransport

* Expose timeouts used by HTTPServiceImpl

* Add additional documentation to HTTPService

* Remove MockedHTTPService

* Fix missing license

app/server.go

@@ -425,9 +425,6 @@ func (s *Server) Shutdown() error {
 
 	s.DisableConfigWatch()
 
-	if s.HTTPService != nil {
-		s.HTTPService.Close()
-	}
 	mlog.Info("Server stopped")
 	return nil
 }