Remove legacy zaaktype/documenttype URL fields in registration backends

[sergei-maertens]

Currently we support he indirect references by using omschrijving/identificatie and the legacy explicit version URLs for documenttypes/zaaktypes in the Objects API and ZGW API's registration. The latter can be removed as a cleanup.

NOTE

This requires the file upload component URL references to be replaced with documenttype descriptions too, and made context-aware of the registration backend that they're used by (moving out of formio builder into the variables tab).

Tasks

• Add detection script/upgrade check blocking upgrades if legacy fields are still used somewhere
• Delete the fields ZaakOptionsSerializer.zaaktype, ZaakOptionsSerializer.informatieobjecttype, ZaakOptionsSerializer.objecttype
• Delete the fields ObjectsAPIOptionsSerializer.informatieobjecttype_submission_report, ObjectsAPIOptionsSerializer.informatieobjecttype_submission_csv, ObjectsAPIOptionsSerializer.informatieobjecttype_attachment
• Delete the fields ObjectsAPIGroupConfig.informatieobjecttype_submission_report, ObjectsAPIGroupConfig.informatieobjecttype_submission_csv and ObjectsAPIGroupConfig.informatieobjecttype_attachment