allow docker usage

[GersonTrj]

Describe Request:

I would find very useful to be able to run this validator as a docker container so I can run it from my golang project.

[punkle]

This sounds like a nice improvement.

[punkle]

You can no run this:

docker run --rm -v $(pwd):/workdir roadiehq/backstage-entity-validator catalog-info.yaml