Publish tagged images to GHCR

[jpolchlo]

Improvement

Right now, images are published to quay.io, but there are not meaningful tags used to do this. Images are tagged with a SHA, and it might be asking a lot to have a user figure out which SHA represents which milestone. We are also publishing an ungodly amount of images, which seems to contribute nothing but noise. We ought to shift the publishing strategy. It may be useful to add a GH action to publish clearly tagged images to GHCR (the Github Container Repository). We can continue to publish images to quay tagged with SHAs for testing purposes, but given the volume of commits relative to the number of tags, moving official releases to another repository will aid in discoverability. With respect to the quay repository, it might also be better to only publish an image there on a push to a PR or branch. That's more open to debate, though (and may be what's happening already, I'm not savvy to the setup of this repo).

Notes + Context

A downside of this is that it can be hard to get a listing of images in a GHCR collection. We should be sure to document a method in the readme to offer a solution for users (and our future selves) to get a listing of available image tags.

[moradology]

If memory serves, we were also warned by quay about publishing every new head of master with GT. That's another reason to reconsider the current strategy