support for iCal

### What feature is it?

Given the nature of iCal, it would make sense to be able to convert into RSS.

### What problem does this feature solve?

Ical feeds could easily be converted into RSS

### Additional description

See a site like the following. It only offers support for iCal export.

https://luma.com/sf

Converting from iCal to RSS would make access to this information simple.

### This is not a duplicated feature request or new RSS proposal

- [x] I have searched [existing issues](https://github.com/DIYgod/RSSHub/issues) to ensure this feature has not already been requested and this is not a [new RSS proposal](https://github.com/DIYgod/RSSHub/issues/new?assignees=&labels=RSS+proposal&template=rss_request_en.yml).