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/000032_create_sharedchannels.up.sql

@@ -0,0 +1,16 @@
+CREATE TABLE IF NOT EXISTS SharedChannels (
+  ChannelId varchar(26) NOT NULL,
+  TeamId varchar(26) DEFAULT NULL,
+  Home tinyint(1) DEFAULT NULL,
+  ReadOnly tinyint(1) DEFAULT NULL,
+  ShareName varchar(64) DEFAULT NULL,
+  ShareDisplayName varchar(64) DEFAULT NULL,
+  SharePurpose varchar(250) DEFAULT NULL,
+  ShareHeader text,
+  CreatorId varchar(26) DEFAULT NULL,
+  CreateAt bigint(20) DEFAULT NULL,
+  UpdateAt bigint(20) DEFAULT NULL,
+  RemoteId varchar(26) DEFAULT NULL,
+  PRIMARY KEY (ChannelId),
+  UNIQUE KEY ShareName (ShareName, TeamId)
+) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;