Mono repo -> Master (#22553)

Combines the following repositories into one:

https://github.com/mattermost/mattermost-server
https://github.com/mattermost/mattermost-webapp
https://github.com/mattermost/focalboard
https://github.com/mattermost/mattermost-plugin-playbooks

server/channels/wsapi/system.go

@@ -0,0 +1,22 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+
+package wsapi
+
+import (
+	"github.com/mattermost/mattermost-server/v6/model"
+)
+
+func (api *API) InitSystem() {
+	api.Router.Handle("ping", api.APIWebSocketHandler(ping))
+}
+
+func ping(req *model.WebSocketRequest) (map[string]any, *model.AppError) {
+	data := map[string]any{}
+	data["text"] = "pong"
+	data["version"] = model.CurrentVersion
+	data["server_time"] = model.GetMillis()
+	data["node_id"] = ""
+
+	return data, nil
+}