Common report format for Container Scanning

Problem to solve

With https://gitlab.com/gitlab-org/gitlab-ee/issues/9244 we have a wrapper around Clair to provide Container Scanning.

The report format is still the original one, and we need to make it compatible with our Common Analyzers API.

This will allow more flexibility in changes. It will also add version information.

Proposal

Change our Container Scanning image to create a new report format following our Common Analyzers API.

We still need to guarantee backward compatibility until we'll eventually remove the old format, but we can deprecate it as soon as this is ready.