Add version-tagged docker image

[legoraft]

Currently, all docker images are just tagged with the commit hash. I'm using renovate to update my docker images and it doesn't play nice with commit hash versions. Because SemVer is already used for full releases, I was wondering if the docker images of those releases could also be tagged with SemVer, to make updating easier.

[robinbraemer]

Hey cool would you be open to try a PR to add it? :)

[legoraft]

Hi thanks for implementing this! I was looking to make a PR, but didn't really get the ci workflow so went for an issue instead. Thanks a lot for the update!