Entity Pay - Update to work with alternate name changes

Update entity-pay 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.

Note that as it currently stands, the queue message being sent to the filer from entity-pay does not match the message structure that the filer expects. Update the message entity-pay sends to match the what filer expects.

Filer expects this message format:

```json
{
"specversion": "1.0",
"datacontenttype": "application/json",
"source": "business_pay",
"subject": "filing",
"type": "filingMessage",
"data": {
"filingMessage": {
"filingIdentifier": 123
}
}
}
```

**TODOs**
- [ ] Do work in legal name branch
- [ ] Update to work with alternate names and legal entities
- [ ] Update queue message structure sent to filer to match what filer expects
- [ ] There may be some other misc updates required to get processor working. Update as appropriate.
- [ ] Update worker.py as required
- [ ] Update tests as appropriate