MM-31401 Add Shared flag to Channels table (#16568)

* add Shared flag to Channels table

store/sqlstore/upgrade.go

@@ -956,6 +956,7 @@ func upgradeDatabaseToVersion531(sqlStore *SqlStore) {
 	// if shouldPerformUpgrade(sqlStore, VERSION_5_30_0, VERSION_5_31_0) {
 	// allow 10 files per post
 	sqlStore.AlterColumnTypeIfExists("Posts", "FileIds", "text", "varchar(300)")
+	sqlStore.CreateColumnIfNotExistsNoDefault("Channels", "Shared", "tinyint(1)", "boolean")
 	// saveSchemaVersion(sqlStore, VERSION_5_31_0)
 	// }
 }