Allow Calendar to automatically sync all newly-added CalDAV calendars rather than force the user to add them manually.

[RokeJulianLockhart]

Checklist

• [X] I made sure that there are no existing issues - open or closed - to which I could contribute my information.
• [X] I made sure that there are no existing discussions - open or closed - to which I could contribute my information.
• [X] I have read the FAQs inside the app (Menu -> About -> FAQs) and my problem isn't listed.
• [X] I have taken the time to fill in all the required details. I understand that the bug report will be dismissed otherwise.
• [X] This issue contains only one feature request.
• [X] I have read and understood the contribution guidelines.
• [ ] I optionally donated to support the Fossify mission.

Feature description

Calendar should poll the AOSP calendar store automatically and commence synchronization.

Why do you want this feature?

When I add a new CalDAV calendar to my device, I must enter FOSSify Calendar to enable sync manually. I shouldn't need to.

Additional information

Of course, allow the user to disable this, but it should be defaulted to on.