Cache the Docker container

[prestoncarman]

Currently, the action builds the docker file each time the action is run. Can the build Docker container be cached so it is just downloaded each time?

[ianfixes]

I believe that's in progress on GitHub's end, I was pretty surprised they weren't exploiting a layer cache during their builds
https://github.community/t/cache-a-docker-image-built-in-workflow/16260/2