Update eluceo/ICal dependency to the new version

[pascalchevrel]

We use an old version (0.16) of https://packagist.org/packages/eluceo/ical because when I implemented the calendar features, the newer iCal version (2.* a complete rewrite) had dependencies conflicting with some of the other dependencies we have in the project.

That was 18 months ago, since then we have had multiple updates of our dependencies, moved from php 7.4 to 8.1, we should see if we can use the newer version.

• Identify what the dependency clash was and see if it is fixable
• update iCal to 2.*
• rewrite our code to use the new API (not backward compatible)