Replace container_scanning job definition with a vendored template

Problem to solve

Job definition for ~"container scanning" is frozen, and can't be easily updated without creating breaking changes.

Further details

With https://gitlab.com/gitlab-org/gitlab-ce/issues/53445, we'll be able to ship a template embedded with each version of GitLab. The template can be updated from one version to another, without impacting our users.

Proposal

What does success look like, and how can we measure that?

The new official job definition is a single inclusion instruction:

include:
  template: Container-Scanning.gitlab-ci.yml

(see the discussion and final syntax)

Links / references

Execution

• Add the Container-Scanning.gitlab-ci.yml with the contents from the example to the templates dir under Security subdir
• Test in the development environment on a test project
• Update the ~Documentation for the Container Scanning CI configuration
  • docs page, see https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/9875
  • security products release process (add a section to check the vendored template are up-to-date)