Provide calendar feed for scheduled maintenance updates within status.heroku.com

### Required Terms

- [X] I agree to follow this project's [Code of Conduct](https://github.com/heroku/roadmap/blob/main/CODE_OF_CONDUCT.md)
- [X] I have read and accept the [Salesforce Program Agreement](https://www.salesforce.com/company/program-agreement/)

### What service(s) is this request for?

Heroku Status

### Tell us about what you're trying to solve. What challenges are you facing?

Right now, when a scheduled maintenance update gets posted to status.heroku.com, it currently only triggers one notification for any integration (e.g. email or slack), which is easy to miss in a deluge of other service status updates. Instead, it would be great if the feed of upcoming maintenance items could be provided as an ical feed so that customers could add it to their own internal calendars and get updates / reminders as scheduled maintenances get closer.

I think this was discussed at the CAB session in March, haven't heard anything since then.