Fixing Docker Hub publishes

[danjbh]

what?!

I had originally modeled the Github action build triggers against another project, and upon further analysis, I don't think the project I modeled is actually working properly. In a nutshell, the release created trigger wasn't firing when the auto-release workflow was executed, which means we were never getting Docker images with actual semver tags in Docker Hub.

In addition, I had to cleanup some of the expression logic to properly match github.ref.

Anyhow, I was able to test it in my branch before merging to master by just pushing a new tag, and I'm happy to report it's working. Here's the behavior...

• If you're pushing a new commit against a non-forked PR, it will build/push a new image to Docker hub (with both an sha-<sha> AND a pr-<num>-merge tag
• If a new tag (or release) is created, it will build an image and upload it to Docker hub using the proper semver format (generated by auto-release, but without the leading v)

What I haven't tested is the auto-release portion, but I'm fairly certain it should work with this method. Of course, I thought the past couple attempts would work, and I think I'm starting to question my own sanity at this point.