Create `latest_release` Docker image tag during release process

[2opremio]

It should point to the latest release. To be used when integrating with third-party projects (and make sure they don't bitrot).

[rade]

To be clear, we are talking about image tags on dockerhub et al, rather than git tags, right? Since we already have a latest_release for the latter.

[2opremio]

To be clear, we are talking about image tags on dockerhub et al, rather than git tags, right?

Yep. Sorry I wasn't specific enough