[Feature] Add calendar public flag option

[1Luc1]

Add a .env flag PUBLIC_CALENDAR_ENABLED which will show or hide the public selection for calendar. Related to PR #105.

[1Luc1]

@tchapi for the PHPUnit test to run correctly the public_calendar_enabled options has to be set. Has to be there an entry within .env.test with PUBLIC_CALENDAR_ENABLED=false so it does pass?

[tchapi]

Thanks for the PR 🙏🏼

We also need to make sure that calendars are not public when the option is set to False, which means modifying the PublicAwareDAVACLPlugin acls so that it honours the env var:

if ($calendar && $calendar->isPublic() && $public_calendar_enabled) {
// ...
}

[tchapi]

Note: I renamed it to PUBLIC_CALENDARS_ENABLED (with an S)