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/entrypoint.sh

@@ -0,0 +1,7 @@
+#!/bin/bash
+
+if [ "${1:0:1}" = '-' ]; then
+    set -- mattermost "$@"
+fi
+
+exec "$@"