EXTERN: 414 URI too long when syncing moderately complex data model

extern: https://gitlab.com/linkahead/linkahead-advanced-user-tools/-/issues/55

See the xfailing integration test in caosdb-advanced-user-tools@c8c555b2:

        dm = DataModel()
        long = "Long" * 50
        first_RT = db.RecordType(name=f"TestRecord_first")
        for index in range(20):
            this_RT = db.RecordType(name=f"TestRecord_{long}_{index:02d}")
            first_RT.add_property(this_RT)
            dm.append(this_RT)
        dm.append(first_RT)
        dm.sync_data_model(noquestion=True)  # Insert
        dm.sync_data_model(noquestion=True)  # Check again

• Fixed or usable workaround.
• Followup issues created if necessary