PLT-8086 Fix plugin config watcher for enabling and disabling (#7770)

* Fix plugin config watcher for enabling and disabling

* Make sure HTTP routes are served

* Set content-type explicitly

cmd/platform/server.go

@@ -75,6 +75,13 @@ func runServer(configFileLocation string) {
 
 	if webappDir, ok := utils.FindDir(model.CLIENT_DIR); ok {
 		a.InitPlugins(*a.Config().PluginSettings.Directory, webappDir+"/plugins")
+		utils.AddConfigListener(func(prevCfg, cfg *model.Config) {
+			if *cfg.PluginSettings.Enable {
+				a.InitPlugins(*cfg.PluginSettings.Directory, webappDir+"/plugins")
+			} else {
+				a.ShutDownPlugins()
+			}
+		})
 	} else {
 		l4g.Error("Unable to find webapp directory, could not initialize plugins")
 	}