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

webapp/channels/build/notice-file/README.md

@@ -0,0 +1,35 @@
+# Notice.txt File Configuration
+
+We are automatically generating Notice.txt by using first-level dependencies of the project. The related pipeline uses `config.yaml` stored in this folder.
+
+
+## Configuration
+
+Sample:
+
+```
+title: "Mattermost Web App"
+copyright: "© 2017-present Mattermost, Inc.  All Rights Reserved.  See LICENSE.txt for license information."
+description: "This document includes a list of open source components used in Mattermost Web App, including those that have been modified."
+reviewers: 
+  - "mattermost/release-managers"
+  - "mattermost/web-platform"
+search:
+  - "package.json"
+  - "packages/**/package.json"
+dependencies: 
+  - "wix"
+devDependencies: 
+  - "webpack"
+```
+
+| Field | Type   | Purpose |
+| :--   | :--    | :--     |
+| title | string | Field content will be used as a title of the application. See first line of `NOTICE.txt` file. |
+| copyright | string | Field content will be used as a copyright message. See second line of `NOTICE.txt` file. |
+| description | string | Field content will be used as notice file description. See third line of `NOTICE.txt` file. |
+| reviewers | array of GitHub user/teams | Those will be automatically assigned to the PRs as reviewers. |
+| dependencies | array | If any dependency name mentioned, it will be automatically added even if it is not a first-level dependency. |
+| devDependencies | array | If any dependency name mentioned, it will be added when it is referenced in devDependency section. |
+| search | array | Pipeline will search for package.json files located. Globstar format is supported `packages/**/package.json`. |
+