Feature request: support user-defined property

[jkischel]

Is your feature request related to a problem? Please describe.
I'm synchronizing my nextcloud contacts with other programs and devices (e.g. my Android phone). These third party .vcf software also uses customized fields (e.g. for a customized ringtone).

Describe the solution you'd like
It would be great to support user-defined property types. I'm not sure if it would be senseful to define them globally or in one special contact. Maybe you could add a "other properties" category.

Yes, this would be an expert feature, no question. But supporting non-standardized has some advantages: fields that are not yet supported can already be used. Existing non-standard fields (hopefully) don't get destroyed and can be changed.

Describe alternatives you've considered
Well, what fields other applications are using is normally not the choice of the user.

Additional context
This could look like this:

[skjnldsv]

Hey :)

Please have a look at #1045
This is very similar. Basically we cannot do that as we don't know the format of the properties used here. So it would be very risky and could lead to data loss.
See last message of #1045

Sorry! And thanks again for your interest in contacts 😉