add oci labels

[grooverdan]

Closes #436

Reference for labels https://github.com/opencontainers/image-spec/blob/main/annotations.md#pre-defined-annotation-keys

[grooverdan]

against https://snyk.io/blog/how-and-when-to-use-docker-labels-oci-container-annotations/:

• org.opencontainers.image.source - done
• org.opencontainers.image.revision - not done. Could be, if included in the downloads API, or pulling the tag lookup on the github API
• org.opencontainers.image.base.digest - not done. Its dependant on the Docker Library release process to pull the exact mapping of the ubuntu base into the labels during build. There's no auto build arg populated with this digest.
• org.opencontainers.image.base.name - done

Custom labels, haven't really considered, org.mariadb.releasenotes might be an option.

Unsure how verbose to go with org.opencontainers.image.description

[grooverdan]

@tianon @yosifkit , I haven't seen anything on guidance for labels/annotations. docker best practices does have a label section, however beyond reverse domain notation for keys not much is mentioned. Do you have any guidance?

Do you want org.opencontainers.image.vendor to contain Docker Library or any other changes?

[tianon]

See https://github.com/docker-library/official-images/issues/3540#issuecomment-530925319, especially:

We don't actively recommend using labels. If an image maintainer wants to have labels, that is fine, but label names should adhere to the image spec: https://github.com/opencontainers/image-spec/blob/v1.0.1/annotations.md