Docker files to replicate aws build and deployment

[samhstn]

For easier production release debugging, it would be helpful to be able to locally replicate:

• the codebuild steps which build the mix release.
• the ec2 instance which runs the mix release.

This could be nicely achieved with:

• a build.Dockerfile for building the release.
• a run.Dockerfile for running the release.
• a docker-compose.yml file for sharing volumes and coordinating these files.