More intelligent CI for images

[davenquinn]

Following on #207, we no longer have the issue of tedious builds in runtime. However, Docker image builds are still slow. Some of this can be solved with improvements to our CI configuration. Specifically:

• Docker image builds should better make use of the layer cache, not just the module cache
• We should ensure the layer cache is loaded effectively in Github CI
• The Production and development CI tasks should be unified – they both do the same bundle process, only applying different tags to the built image
• It seems to take a long time to upload to Harbor; is this normal?