Send `event-reminders-hourly` notification to `#vc-events` and optional second channel

Related to https://github.com/Virtual-Coffee/cms.virtualcoffee/issues/11 ([see comment](https://github.com/Virtual-Coffee/cms.virtualcoffee/issues/11#issuecomment-2181179231))

_All_ hourly notifications should be `#vc-events`. If the event has `eventSlackAnnouncementsChannelId` set (and that value is not the same as `DEFAULT_SLACK_EVENT_CHANNEL`, _also_ send it to that channel