Integrate EteSync into Phosh / Plasma Mobile on postmarketOS

EteSync is a free software server and protocol, which provides end-to-end encrypted calendar and contact synchronization.

This would be a good improvement over existing caldav/carddav providers, as those only encrypt the connection to the server, but do not encrypt the actual contents of the calendar / contacts data.

Let's package it for Alpine and create guides for the postmarketOS wiki on how to use it with Phosh and Plasma Mobile. In theory, we would need to package etesync-dav as caldav/carddav "adapter" and then add that in Phosh (GNOME online accounts) / Plasma Mobile.