ci: update docker workflow semver tags

[krohrsb]

Updates the docker meta workflow to add additional tags, namely semver.

The goal is to have versioned tags on top of the "latest" provided.

[timothymiller]

Does this establish versioning beyond the latest tags?

[krohrsb]

Yes. That is my understanding.

[krohrsb]

https://github.com/docker/metadata-action#semver is the configuration for the docker metadata action.

The idea here is that when you push a release/git tag it would then also create major.minor and major.minor.patch docker tags, in addition to latest.

[adamantike]

Looking forward to see this merged! At the moment, this container is the only one I use where I'm forced to use latest or an image digest, instead of a semver tag.