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/build/notice-file/config.yaml

@@ -0,0 +1,11 @@
+---
+
+title: "Mattermost Server"
+copyright: "©2015-present Mattermost,Inc. All Rights Reserved. See LICENSE for license information."
+description: "This document includes a list of open source components used in Mattermost Server, including those that have been modified."
+search:
+  - "go.mod"
+dependencies: []
+devDependencies: []
+
+...