Create CI Lint API endpoint scoped to project

In !37134 (merged) we expanded the CI Lint to use a dry run mode which goes deeper in the pipeline creation stack, providing a simulation of the actual pipeline creation.

The dry run mode was implemented only for Projects::Ci::LintsController#create while the API endpoint still uses the legacy method via YamlProcessor. Converting the existing API endpoint to use dry run is not possible because it's project agnostic. The dry run is project-aware.

To solve this problem we could introduce a new API endpoint scoped to projects: POST v4/projects/:id/ci/lint which would have dry run on by default.

This endpoint should return:

{ 
  status: 'failed', # or success
  errors: [ ... ],
  warnings: [ ... ],
  jobs: [ ... ] # if status: success
}