Add grype GH action for testing generated images

[fabriciojs]

Security is an important subject that we don't wanna miss on.

New tools are appearing aiming at testing container images for known vulnerabilities. grype
is one, and would be great to add the checking step to our CI after we build our images, and before we upload them to hub.docker.com.

grype GH action documentation: https://github.com/anchore/scan-action