MM-52600: [Shared Channels] Shared channels do not sync channel membership (#30976)

server/channels/db/migrations/postgres/000140_add_lastmemberssyncat_to_sharedchannelremotes.down.sql

@@ -0,0 +1,2 @@
+ALTER TABLE sharedchannelremotes DROP COLUMN IF EXISTS lastmemberssyncat;
+ALTER TABLE sharedchannelusers DROP COLUMN IF EXISTS lastmembershipsyncat;

server/channels/db/migrations/postgres/000140_add_lastmemberssyncat_to_sharedchannelremotes.up.sql

@@ -0,0 +1,2 @@
+ALTER TABLE sharedchannelremotes ADD COLUMN IF NOT EXISTS lastmemberssyncat bigint DEFAULT 0;
+ALTER TABLE sharedchannelusers ADD COLUMN IF NOT EXISTS lastmembershipsyncat bigint DEFAULT 0;