Extend Birthday calender from contacts with other dates (X-ABDATE)

Is your feature request related to a problem? Please describe.

I like the birthday calendar as I do not need to manage birthdays manually in the calendar. It would be a great feature if the other dates stored with contacts could be included as well. This includes anniversary dates or birthdays of the kids of a contact - whatever one choses to store in the X-ABDATE/X-ABLABEL.

Describe the solution you'd like

If a contact has additional dates added, these could be added to the calendar just like birthdays. They should include the label of the entry. For example: Richard Stallmann (71) for the birthday and Richard Stallmann: GNU Manifesto (39) for the added X-ABDATE with X-ABLABEL "GNU Manifesto". There could be more dates added, like anniversary, the birthday of wife or kids, etc.

Describe alternatives you've considered

Including these dates to the calendar could be an option to (de)activate in settings.

Additional context

An example for a contact with a birthday and an additional date added (multiple are possible):

BEGIN:VCARD
VERSION:3.0
PRODID:-//Sabre//Sabre VObject 4.5.4//EN
UID:6acfa7d3-d1dc-4750-9dce-908bff3232d2
FN:Richard Stallmann
N:Stallmann;Richard;;;
BDAY:19530316
ITEM1.X-ABLABEL:GNU Manifesto
ITEM1.X-ABDATE:19850101
REV:20240328T061445Z
END:VCARD

Search the calendar's birthday-generation entry point and trace how contact VCARD data becomes calendar events. Use the supplied VCARD example to check X-ABDATE and X-ABLABEL handling, then verify that labeled additional dates appear like birthdays and that any activation setting is reflected in the calendar behavior.