Feature Request: Expose verifying signatures via GitHub Actions owner & repo

[viccuad]

Is your feature request related to a problem?

As supported in policy-server and verification config, support verifying signatures performed in GitHub Actions.

Needs kubewarden/policy-sdk-rust#41
Blocks kubewarden/policy-fetcher#91

Solution you'd like

Support a new type of signature in settings:

signatures:
  - image: "*"
    GitHubActions: 
      - owner: octocat
      - repo: test-repo # optional
    annotations: #optional
      env: prod

This will make use of the v1/verify callback with the new CallbackRequestType::SigstoreGithubActionsVerify{}.

Alternatives you've considered

No response

Anything else?

No response