✨ Use floating tag latest instead fixed version tags

[indigo423]

We have introduced the latest floating tag which references the last stable release of Horizon. We can use this as the default.

Pro: New people automatically get the latest stable release
Con: As soon they have a version longer running, they might get updates on the docker pull and have to do config upgrades
Mitigation: As people want to run them for a longer period of time, give them hints to pin the image tags to a specific version to avoid unplanned updates.