Revert "Merge branch 'switch-to-debian' into 'registry'"

This reverts merge request !175 (merged) and cleans up the Dockerfile:

• Compiles hugo from source since the binaries don't work with Alpine https://github.com/gohugoio/hugo/issues/10839
• Remove muslstack patch 22f0d5cb, no longer needed
• Use Alpine 3.16 as the final image (the same image upstream uses https://github.com/gohugoio/hugo/blob/b0b1b76dc9c7edad15924785d01684e36f3e6cdb/Dockerfile#L29)