Enhancement proposal: Add support for hiding data from calendar copies

This is about calendar sync only ;)

I am looking for a system to sync my private calendar with a Google calendar. Due to data protection policies and European laws, I cannot just transfer all these private information into Google without consent of the people mentioned in the private calendar entries.
On the other hand, I need to track my availability in Google calendar to support our partners using the Google calendar to see when I may have some spare time for them.

So the idea is extending vdirsyncer to hide some or all data and just create dummy entries to show that there is something.

I suggest to have the storage configuration section extended to supprt a keyword like create with contents ['normal','title','blocker'] to trigger the storage writer to write

• normal - normal operation
• title - write full titles but nothing else
• blocker- just create an empty blocking entry of same length and title e.g. "Private"

This way, the data retrieved by vdirsyncer remains unchanged and only data written to the exposed storage gets anonymized.

No files, tests, or entry points are identified in the issue. Begin by locating the storage configuration and calendar-sync writer paths. Done would mean supporting the proposed normal, title-only, and blocker output modes while leaving retrieved data unchanged.