Support transparent running against ghcr.io

**Is your feature request related to a problem? Please describe.**
When building containers we are not able to publish the container sandbox image to cvmfs (the preferred and most efficient approach to loading containers in CI). In those cases we only have the full container as pushed to ghcr.io. In order to test the repositories that use this action with containers on ghcr.io we want to be able to transparently fall through from cvmfs to ghcr.io.

**Describe the solution you'd like**
When a release:platform is not found under the respective directory on cvmfs, we should start a docker container that is used to exec the specified commands in. As in the case of cvmfs containers, the docker containers should continue to exist through to the post cleanup.

**Describe alternatives you've considered**
The alternative of requiring changes in all places that use this action is imposing a large amount of responsibility on the downstream users.