Add caching to improve build time performance

[adamus1red]

Uses the builtin cache-from/cache-to options from the docker/buil-push-action to write out the buildx cache. Using the github actions/cache action the buildx cache is stored by github for future runs.

[qdm12]

Hey there, thanks for your PR!

However, having toyed around with buildx caching a few months ago, it always turned out to be slower than without cache, at least for Go projects where things are usually quick to download/test/build. What do you think? I can merge it and compare publish time by doing another commit on top too.

If that turns out to be faster, I can modify the verify job to use buildx and we can try adding caching there too.