create build action

[jprosser]

We no longer have Travis and need to replace with Github Actions here.

[miker985]

I've added this workflow to push new images to GHCR when a "release" is made.

I feel like it's a reasonable solution for explicit releases, but still leaves a gap in "how do we test it before releasing it?"

I was thinking an additional workflow for periodic build + transitory tag like "trunk" would be good to cover that case. "latest" would be technically correct but I'm not sure we want to use that. Thoughts?

[jprosser]

Couple toughts here, first we can probably just go with a lock on major for the actions, for example just docker/metadata-action@v4 instead of v4.4.0, for each of the actions since we're already behind on some.

On latest, perhaps just leave that tag manual for the time being, which means anchored on last known good as manually determined by someone. Once tests can prove it to a reasonable degree, then additionally tag that version as latest in the automation if we get that far along with things.