Add Settings window to Agent UI

Agent systray UI has been extended with
a setting window that allows configuring 
management URL, admin URL and 
supports pre-shared key.
While for the Netbird managed version 
the Settings are not necessary, it helps
to properly configure the self-hosted version.

client/cmd/testutil.go

@@ -93,7 +93,7 @@ func startClientDaemon(
 	}
 	s := grpc.NewServer()
 
-	server := client.New(ctx, managementURL, configPath)
+	server := client.New(ctx, managementURL, adminURL, configPath, "")
 	if err := server.Start(); err != nil {
 		t.Fatal(err)
 	}