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/db/migrations/postgres/000083_threads_threaddeleteat.up.sql

@@ -0,0 +1,5 @@
+-- Drop any existing DeleteAt column from 000081_threads_deleteat.up.sql
+ALTER TABLE threads DROP COLUMN IF EXISTS deleteat;
+
+ALTER TABLE threads ADD COLUMN IF NOT EXISTS threaddeleteat bigint;
+UPDATE threads SET threaddeleteat = posts.deleteat FROM posts WHERE threads.threaddeleteat IS NULL AND posts.id = threads.postid;