Support GitLab Code Quality format

[alessio-locatelli]

https://docs.gitlab.com/ci/testing/code_quality/

The idea is that the review report can be included as an MR code quality report, which creates less noise (each new comment equals an email/RSS notification) and generally improves the MR flow due to native integration.

[mrT23]

Things that create 'less noise' are also easier to ignore.

We have spent time and effort making the output of pr-agent into a more compact way - a single unified table instead of inline code suggestions.

you are free to implement whatever you want in your fork, but putting it into a more general 'report', one of many other sections, is not the way to go IMO. it will just cause the feedback to be ignored.