Write findings as a GitLab Code Quality report

[tauanbinato]

What and why

Phase 3 of the roadmap: --format gitlab prints a GitLab Code Quality report, so merge requests show JevGate's findings in the widget and on the changed lines.

• Issues are the findings --format github annotates (new, not notes): description (message and next step), check_name (rule ID), fingerprint (JevGate's, or a hash of rule, path and line when a finding has none), severity (major when it fails the gate, minor otherwise) and location.path/lines.
• Not allowed with --watch, like the other document formats.
• The site's CI page shows a merge request pipeline that installs a release binary, keeps the answer cache and uploads the report; the output page lists the format.

How it was checked

Unit test for severity, location, lines and both fingerprint cases; a dry run prints []. The pipeline example follows GitLab's documented artifacts:reports:codequality, but hasn't run on GitLab.