Members/Public should recieve automated event promotional notifications and option to recieve event reminders

[afewell]

User Story: Event creators and constituents should be able to receive timely alerts and notifications of upcoming events with little to no manual intervention.

Plan: Currently scoping 3 features to fulfill this requirement, may add more as needed during further discovery and buildout.

1. When new event is created, an entry is added to a separate daily cron workflow that iterates through events and sends an orchestrated sequence of announcement notifications at T-n time before the event. This may include posting tweets at t-7days, t-2 days, t-1day, t-n_hours and also linkedinposts at a possibly different cadence and also messages posted to the community github message board, and possibly other promotional channels.
2. Attach independent ICS files to each event, ideally create an automated process for event entry that automates creation and posting of the ICS file.
3. Ensure that the automated newsletter project is updated to include links to events that occurred within the past week and also to promote upcoming events for ~2 weeks out.