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/000076_upgrade_lastrootpostat.up.sql

@@ -0,0 +1,50 @@
+DO $$
+BEGIN
+	IF (
+		SELECT count(*)
+		FROM information_schema.columns
+		WHERE table_schema=current_schema()
+		AND table_name='channels'
+		AND column_name='lastrootpostat'
+		AND (column_default IS NULL OR column_default != '''0''::bigint')
+	) = 1 THEN
+		ALTER TABLE channels ALTER COLUMN lastrootpostat SET DEFAULT '0'::bigint;
+	END IF;
+END$$;
+
+DO $$
+BEGIN
+	IF (
+		SELECT count(*)
+		FROM Channels
+		WHERE LastRootPostAt IS NULL
+	) > 0 THEN
+		-- fixes migrate cte and sets the LastRootPostAt for channels that don't have it set
+		WITH q AS (
+			SELECT
+				Channels.Id channelid,
+				COALESCE(MAX(Posts.CreateAt), 0) AS lastrootpost
+			FROM
+				Channels
+			LEFT JOIN
+				Posts
+			ON
+				Channels.Id = Posts.ChannelId
+			WHERE
+				Posts.RootId = ''
+			GROUP BY
+				Channels.Id
+		)
+		UPDATE
+			Channels
+		SET
+			LastRootPostAt = q.lastrootpost
+		FROM
+			q
+		WHERE
+			q.channelid = Channels.Id AND Channels.LastRootPostAt IS NULL;
+
+		-- sets LastRootPostAt to 0, for channels with no posts
+		UPDATE Channels SET LastRootPostAt=0 WHERE LastRootPostAt IS NULL;
+	END IF;
+END $$;