Emailer - update amalgamation notification processor to work with alternate name changes

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 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

Start by locating the email processor(s), worker.py, and the tests relevant to this ticket, then review the legal name branch and existing legal_entity handling. Compare the current versioning logic with the new alternate_name model; done means alternate names and legal entities are processed correctly, required versioning is updated, and the relevant tests pass.

Written by the indexing model from the issue text.