chore: add missing OCI LABELs, as reported by GHCR

[michalrus]

Context

You can see GHCR / GitHub Packages complaining here:

• https://github.com/blockfrost/blockfrost-platform/pkgs/container/blockfrost-platform/355296410?tag=0.0.1
• https://github.com/orgs/blockfrost/packages/container/blockfrost-platform/settings

Here's the standard for reference:

• https://github.com/opencontainers/image-spec/blob/main/annotations.md