Publish latest tag for Merlin Docker images.

## Describe the solution you'd like

Currently, all Merlin Docker images are tagged with the Merlin release version and there's no `latest` tag.

## Describe alternatives you've considered

To publish the `latest` tag for all Merlin Docker images on every release.

## Additional context

https://github.com/caraml-dev/merlin/pull/514#discussion_r1442699626