Pass license to OCI image metadata

[joonas-fi]

Cannot take this from GitHub's API because:

1. Vendor lock-in
2. It is not built for current revision
   • Thus on commit where we'd be changing the license, the built image could still be built with the outdated license info.

Idea: have this knowledge be stored in turbobob.json (based on autodetection?) along with some digest of the LICENSE file so we could detect if info is outdated.

[joonas-fi]

It is not built for current revision

OTOH the approach is ok for https://github.com/docker/metadata-action so could be OK for us until we have time to implement more robust way?

[joonas-fi]

This is being worked on in branch: https://github.com/function61/turbobob/tree/feature/license-metadata-and-detector

The above mentioned autodetection adds ~ 12 MB to binary size.

=> make license autodetection a container and only have container launch interface between Turbo Bob and the detector so we don't have to force-ship something that gets ran relatively rarely.