Update Docker Github actions

[cjfields]

At the moment, we're autogenerating Docker builds and uploading them to the Github Docker Registry. However these are primarily tagged to the branch (master, dev) and don't seem to have an associated tag. We may want to update this to the following:

https://github.com/marketplace/actions/docker-build-tag-push

Additionally, we may want to create a branch that is specifically for testing docker updates and take out the automated builds from dev and master (e.g. only build on the docker branch and with tagged releases).

[cjfields]

CI is definitely working on master but not on dev, so need to compare the files when I have time.