feat: add support of Gitlab's sections for CODEOWNERS (#29202)

[MaximeMorille]

Changes

Add support for Gitlab's sections in CODEOWNERS files, notably their default approver feature.

Context

Closes #29202

Documentation (please check one with an [x])

• I have updated the documentation, or
• No documentation update is required (not so sure about that, but I didn't find a part worthy of update)

How I've tested my work (please select one)

I have verified these changes via:

• Code inspection only, or
• Newly added/modified unit tests, or
• No unit tests but ran on a real repository, or
• Both unit tests + ran on a real repository

[rarkins]

Does GitLab's approach conflict with other platforms, particularly GitHub? This change is in lib/workers which means it will apply to all platforms

[MaximeMorille]

Good point, it does conflict with Gitea format.

I will take a look at the platform folder to see if there is a way to implement this only for Gitlab.