Emailer - Update to use new models module

After https://github.com/bcgov/entity/issues/23124 is done, the new models module can now be used with all BE components. The idea is we want to reference the new models module now instead of the models in Legal API.

Need to handle:
- [ ] update requirements.txt to reference models module
- [ ] update code references to refer to new models module
- [ ] any other required updates
- [ ] fix unit tests