use GHA layer caching when building docker images

[megahirt]

See https://github.com/docker/build-push-action for documentation

Our CI docker build process has to build our images from scratch every time because there is no layer caching available. Utilizing caching should speed up our image build considerably.

[rmunn]

We currently aren't using the build-push-action, relying instead on docker compose build to build the entire dependency tree for us. I estimated this task as Tiny at first, but now that I realize that it would involve a larger rewrite of the GHA workflow, I'm bumping the estimate to Small as it will require quite a bit of testing to make sure we got the details right.

[hahn-kev]

Looks like we can do something like this to solve our problem
https://stackoverflow.com/a/75544124/1620542

then for the cache to and from we can probably use some of the patterns defined here
https://docs.docker.com/build/ci/github-actions/cache/

this means we don't need to rewrite our build workflow or anything like that.