Plugins: Register management endpoints only when external managed is also false (#51802)

* Only define plugin install endpoints when catalog enabled

* add external check

pkg/api/api.go

@@ -328,7 +328,7 @@ func (hs *HTTPServer) registerRoutes() {
 		apiRoute.Any("/plugins/:pluginId/resources/*", hs.CallResource)
 		apiRoute.Get("/plugins/errors", routing.Wrap(hs.GetPluginErrorsList))
 
-		if hs.Cfg.PluginAdminEnabled {
+		if hs.Cfg.PluginAdminEnabled && !hs.Cfg.PluginAdminExternalManageEnabled {
 			apiRoute.Group("/plugins", func(pluginRoute routing.RouteRegister) {
 				pluginRoute.Post("/:pluginId/install", routing.Wrap(hs.InstallPlugin))
 				pluginRoute.Post("/:pluginId/uninstall", routing.Wrap(hs.UninstallPlugin))