What does this PR change? What problem does it solve?

This PR adds some labels from the OpenContainers Annotations Spec to the Dockerfile.release file.

My main motivation for this change is the org.opencontainers.image.source label which allows Renovate to show the restic changelog and link to the restic repository when creating a PR: https://docs.renovatebot.com/key-concepts/changelogs/#how-renovate-detects-changelogs https://docs.renovatebot.com/modules/datasource/docker/ (see "Source URL support")

However, the metadata can of course also be useful for other services.

Tested with:

• podman build -t test -f docker/Dockerfile.release --platform linux/amd64 .
• podman image inspect --format='{{json .Config.Labels}}' test

Output:

{"io.buildah.version":"1.41.4","org.opencontainers.image.description":"Fast, secure, efficient backup program","org.opencontainers.image.documentation":"https://restic.readthedocs.io","org.opencontainers.image.source":"https://github.com/restic/restic","org.opencontainers.image.title":"restic","org.opencontainers.image.url":"https://restic.net"}

Was the change previously discussed in an issue or on the forum?

No

Checklist

• I have added tests for all code changes. -> no code changes
• I have added documentation for relevant changes (in the manual). -> no documentation necessary
• There's a new file in changelog/unreleased/ that describes the changes for our users (see template).
• I'm done! This pull request is ready for review.