Explore using built-in Docker Compose functionality for orchestration

[mcdonnnj]

💡 Summary

We should look at leveraging functionality available in Docker Compose to control startup order for how we manage the order of containers running in this orchestration.

Motivation and context

We currently rely on each container writing to a redis database (running on a container) to control when containers will actually begin their functionality. We could instead leverage the service_completed_successfully condition for any containers that are simply configured to run after another has completed.

Implementation notes

This should be straightforward for the save, scan, and trustymail_report services as they all have a simple dependency relation. We would need to break out the report archiving functionality in the pshtt_report service to be able to fully do away with using redis for orchestration. I think this would also serve #151 as it would fully remove the need for container-based coordination from this configuration.