Starring contacts

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

A user should be able to star contacts on NextCloud Contacts.

Describe the solution you'd like

Here is what needs to happen:

• A contact can be starred in the nextcloud, which adds it to the starred group
• Removing the star on a contact removes it from the group
• When synchronizing, any new contact that is on the starred group needs to show the star highlighted

Describe alternatives you've considered

No response

Additional context

Who will use this new feature and why?

• Users importing address books from Google contacts, which also use this starred group.
• Users wanting to see their favorite contacts easily in the UI
• Users syncing contacts from mobile devices with contacts apps that follow Google-like approaches to favoriting i.e. add the "starred" category to the vcard will be able to star a contact in their device and be able to see it in their cloud

Start by tracing how Nextcloud Contacts represents contact groups, how the starred group is synchronized, and where contact actions are handled in the UI. Done means starring adds the contact to the starred group, removing the star removes it, and synchronized contacts in that group display as starred.