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/mysql/000096_threads_threadteamid.up.sql

@@ -0,0 +1,35 @@
+-- Drop any existing TeamId column from 000094_threads_teamid.up.sql
+SET @preparedStatement = (SELECT IF(
+    EXISTS(
+        SELECT 1 FROM INFORMATION_SCHEMA.STATISTICS
+        WHERE table_name = 'Threads'
+        AND table_schema = DATABASE()
+        AND column_name = 'TeamId'
+    ) > 0,
+    'ALTER TABLE Threads DROP COLUMN TeamId;',
+    'SELECT 1;'
+));
+
+PREPARE removeColumnIfExists FROM @preparedStatement;
+EXECUTE removeColumnIfExists;
+DEALLOCATE PREPARE removeColumnIfExists;
+
+SET @preparedStatement = (SELECT IF(
+    NOT EXISTS(
+        SELECT 1 FROM INFORMATION_SCHEMA.COLUMNS
+        WHERE table_name = 'Threads'
+        AND table_schema = DATABASE()
+        AND column_name = 'ThreadTeamId'
+    ),
+    'ALTER TABLE Threads ADD COLUMN ThreadTeamId varchar(26) DEFAULT NULL;',
+    'SELECT 1;'
+));
+
+PREPARE addColumnIfNotExists FROM @preparedStatement;
+EXECUTE addColumnIfNotExists;
+DEALLOCATE PREPARE addColumnIfNotExists;
+
+UPDATE Threads, Channels
+SET Threads.ThreadTeamId = Channels.TeamId
+WHERE Channels.Id = Threads.ChannelId
+AND Threads.ThreadTeamId IS NULL;