Feature: CustomData support for groups (since KDBX4)

[tribbin]

KDBX4 has CustomData (String dictionary) fields for PwDatabase, PwGroup and PwEntry. "PwEntry and PwGroup now have a CustomData property. This property has the same type as CustomData of PwDatabase, and is serialized analogously (same XML structure)." (https://keepass.info/help/kb/kdbx_4.html#extobj)

This would enable nice features for projects using your library.
https://gitlab.gnome.org/World/secrets/-/issues/445

[Evidlo]

If you or people from Secrets could suggest an API design that fits with the rest of the library, I'd be happy to implement it.