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/000032_create_sharedchannels.up.sql

@@ -0,0 +1,16 @@
+CREATE TABLE IF NOT EXISTS sharedchannels (
+    channelid character varying(26) NOT NULL,
+    teamid character varying(26),
+    home boolean,
+    readonly boolean,
+    sharename character varying(64),
+    sharedisplayname character varying(64),
+    sharepurpose character varying(250),
+    shareheader character varying(1024),
+    creatorid character varying(26),
+    createat bigint,
+    updateat bigint,
+    remoteid character varying(26),
+    PRIMARY KEY (channelid),
+    UNIQUE (sharename, teamid)
+);