Add 1-way sync (from .ics to WP) for all iCal formats

[Valentina R]

This was said to a customer 10 months ago:

Our devs say that Outlook sync is currently not on the roadmap.
However, we’ll be adding 1-way sync (from .ics to WP) for all iCal formats, even outlook, but I can’t give you a timeline.

Requested here.