Autocomplete and suggest contact on the related field

Is your feature request related to a problem? Please describe.
When a User tries to add a related contact, they are required to enter a URL.
For example:
Contact: Mary Jones
Related:
sibling:https://aaaaaa.aa/aa

The problem is:
a) User does not know what to do with this!
b) Sometimes the User will just want to enter the name of a person or organisation and not provide a linked contact URL
c) Sometimes the User will want to use this field to link a contact to another contact, but there is currently no way to search and enter the UID of another linked contact
d) Common apps that allow this field (such as Android) do not require a URL, and accept free text, which makes sync difficult.

Describe the solution you'd like
When a user selects 'Related' field, besides choosing a pre-built or custom label (i.e. sibling, friend etc...), the user should be able to
a) search for another contact and add it's UID
b) enter a URL (as currently)
c) enter free text to describe a related contact (including one which is not stored in the addressbook).

Additional context
Here is an issue related to that in Thunderbird CardMate client:

https://gitlab.com/CardBook/CardBook/issues/557

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No files or tests are named in the issue. Start by tracing the Related field entry point in the contacts app and review the linked CardBook issue for context. Done should support searching for a contact UID, entering a URL, and entering free text for an unlisted related contact.