refactor(email-service): Separate email api and pubsub workers into separate services

[evanhutnik]

Summary

I would like to not merge this before our prod deploy today/Monday so it has some time to soak in dev before going to prod.

Separate the email api and the email pubsub workers into separate bins/services.

The code still all lives in the email-service crate, but the pubsub workers now have their own bin and fargate service.

This required some refactoring of the pulumi code, namely moving the instantiation of a few things (IAM role, policies, s3 bucket) from service.ts into index.ts.

Both things still use the same Config struct (and env vars) for now.

I had to move some code into modules under lib.rs so it could be accessed by the pubsub_workers bin as well.

Tested locally and in dev.

Screenshots, GIFs, and Videos

[linear]

COMMS-46 Move email workers out of service pods