Add OCI annotations to published container images

[timflannagan]

This issue tracks adding the OCI image spec annotations to our published images. See https://github.com/opencontainers/image-spec/blob/main/annotations.md for more information. This can be done via the ko stanza or via build args in the docker stanza in the goreleaser config. For the latter, we'll likely need to create and push the manifests ourselves as goreleaser doesn't seem to handle this OOTB for us.

[github-actions]

This issue has been marked as stale because of no activity in the last 180 days. It will be closed in the next 180 days unless it is tagged "no stalebot" or other activity occurs.