WIP: 6717 extend reports for security products ee

What does this MR do?

Extend the recent reports feature to support Security Products.

Now sast, dependency_scanning, container_scanning and dast are allowed keys to put in the reports: section of your gitlab-ci.yml.

This MR suggests some refactoring of existing code written for Junit test reports to DRY the common logic.

This MR also provides skeletons for Security reports parsers (they won't parse anything) so that we can validate the architecture and then work on the parsing logic in a dedicated MR.

Please note that Security Reports are EE only feature so this MR add some changes to CE code to allow its extension via EE modules. Once this MR is approved, a backport of these changes will be submitted in another MR on CE.

What are the relevant issue numbers?

#6717 (closed)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• Tests added for this feature/bug
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides
• EE specific content should be in the top level /ee folder
• For a paid feature, have we considered GitLab.com plans, how it works for groups, and is there a design for promoting it to users who aren't on the correct plan?