Emailer - update agm extension 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 covered by this ticket and its worker.py entry point, then inspect the relevant tests and the legal name branch. Confirm how alternate_name and legal_entity are represented and how versioning is handled in the current data model. Done means the processor and worker support the required name changes, versioning is updated where needed, miscellaneous failures are resolved, and relevant tests pass.

Written by the indexing model from the issue text.