Handle missing required fields for BBMs before EnforcedSince for BackgroundMigration/DictionaryFile

!132639 (merged) added checks on required fields in BBM dictionary (enforcedSince: 20231018100907).

We have to try to add those fields for (invalid) migrations before the enforced timestamp.

Also handle Danger warning on existing rubocop:disable BackgroundMigration/MissingDictionaryFile