LPS-45506 Update calendar booking Modified Date while adding or deleting a recurrence exception

Hi Adam! Hope everything is fine :smile:
While working on some synchronization engines for the Calendar portlet, I realized it's not so easy to find when a booking recurrence has changed: I'd like to use dynamic queries to find created and updated bookings, but the `modifiedDate` value isn't updated when a recurrence is changed. Do you think it's possible to add this very small but useful functionality? :blush: