Emailer - update registration processor to work with alternate name changes (DO FIRST)

Update email processor(s) 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 email processor(s) relevant to this ticket:
- [ ] Do work in legal name branch
- [ ] Update to use V2 document endpoint
- [ ] 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 worker.py as required
- [ ] Update tests relevant to this email processor

Locate the email processor(s), worker.py, and their relevant tests in the repository. Start by tracing the current processor flow and its document endpoint and versioning logic, then compare how legal_entity and alternate_name data are handled. Done means the applicable processors support the new model, use the V2 endpoint, and pass updated tests.

Written by the indexing model from the issue text.