Add default value for schedule.timezone upgrades

The value must not be null, so we have to set a default when
upgrading the schema. For that we look for the first
`timeperiod_entry` and use it's `timezone` column. If no entry
exists, the fallback is **'UTC'**.

Author: jrauh01

schema/mysql/upgrades/002.sql

@@ -1 +1,4 @@
-ALTER TABLE schedule ADD COLUMN timezone text NOT NULL;
+ALTER TABLE schedule ADD COLUMN timezone text;
+UPDATE schedule s SET timezone = (SELECT tpe.timezone FROM timeperiod_entry tpe INNER JOIN timeperiod tp ON tp.id = tpe.timeperiod_id INNER JOIN rotation r ON r.id = tp.owned_by_rotation_id WHERE r.schedule_id = s.id ORDER BY tpe.id LIMIT 1);
+UPDATE schedule SET timezone = 'UTC' WHERE timezone IS NULL;
+ALTER TABLE schedule MODIFY COLUMN timezone text NOT NULL;

schema/pgsql/upgrades/002.sql

@@ -1 +1,4 @@
-ALTER TABLE schedule ADD COLUMN timezone text NOT NULL;
+ALTER TABLE schedule ADD COLUMN timezone text;
+UPDATE schedule s SET timezone = (SELECT tpe.timezone FROM timeperiod_entry tpe INNER JOIN timeperiod tp ON tp.id = tpe.timeperiod_id INNER JOIN rotation r ON r.id = tp.owned_by_rotation_id WHERE r.schedule_id = s.id ORDER BY tpe.id LIMIT 1);
+UPDATE schedule SET timezone = 'UTC' WHERE timezone IS NULL;
+ALTER TABLE schedule ALTER COLUMN timezone SET NOT NULL;