Entity BN - Update change of registration flow to work with alternate names

Update bn processor such that we are able to work with alternate_name entries where required. With the new data model, SPs will need to use alternate_name similar to the way we use a legal_entity record.

**TODOs**
Do following for bn processor(s) relevant to this ticket:
- [ ] Do work in legal name branch
- [ ] Update to work with alternate names and legal entities
- [ ] Update versioning logic where required. May be still using versioning approach used in old data model
- [ ] There may be some other misc updates required to get processor working. Update as appropriate.
- [ ] Update LegalEntity, AlternateName and Filings model manually in common models to match with legal api models as required
- [ ] Update worker.py as required
- [ ] Update tests relevant to this bn processor

Start with the bn processor and worker.py, then compare the common LegalEntity, AlternateName, and Filings models with the legal API models. Review the existing tests for this bn processor and the legal name branch before changing alternate-name handling and versioning. Done means the processor supports alternate names and legal entities, the models are aligned, and relevant tests pass.

Written by the indexing model from the issue text.