Add configuration options to utilize new features in mail_room 0.10.0

Specifically:

1. Enable expunging deleted messages. Hard-coded to true, because I'm 99% sure this is the expected behavior. Open to making it configurable
2. Structured logging: it must be explicitly given a log_path to enable it, and /dev/stdout ensures it goes to stdout, which is the most correct option for a container (as I understand things)