Docker images publication workflow

[Tansito]

Related with #690 I was having some discussions with the dev-ops teams related with our publication workflow. Right now what we have is the next one:

• latest: tag for main branch
• x.y.z: semver tag for releases

This makes that we need to run several processes in all the Pull Requests because all the changes that we merge in main are published. The workflow proposed here is the next one:

• x.y.z: semver tag for releases
• latest: tag pointing out to the last release

No tag initially for main but there are tags for those use cases like nightly. I think we can skip it because the current use of main is near to zero. And the benefits that we would receive with this change is:

• Some resources optimization: there are steps in the CI that we could left only for releases and simplify the pull requests.
• Reduce the number of pushes to the registry: they are aware of these numbers, there is no problem right now but just to be aware with.
• More near to the standard: it seems the latest tag is typically used for that purpose. A little near example is ray-image.

I liked the idea and I think it has sense but I would like to know yours!

[psschwei]

I'm totally fine with dropping a build for every commit (and it's easy enough to do locally if one really needs it).

I'd also be ok with dropping the latest tag in general (it's not good practice to use it), but if it's pointing to the last release, then 🤷

We could also think about using digests instead of tags, but that's probably a discussion for another day 😄