Add coverage_report keyword in CI reports

What does this MR do and why?

Introduce a new CI config for coverage report. This sets up for more supported coverage report formats.

artifacts:
  reports:
    coverage_report:
      ​coverage_format: cobertura
      path: ​coverage/cobertura-coverage.xml

This new config is intended to replace artifacts:reports:cobertura as we intend to add more coverage formats. For that reason, CI config must only contain either cobertura or coverage_report, not both.

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Given the following yaml:

test:
    script:
        - echo "stub report" > cobertura.xml

    artifacts:
        reports:
            coverage_report:
                coverage_format: cobertura
                path: cobertura.xml

The job should run successfully and uploads the report as artifact:

How to set up and validate locally

1. Create a new project with CI config that produces a cobertura report
2. Run a pipeline on the project.
3. Validate that the runner uploads the correct report as artifact.

MR acceptance checklist

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Related to #344533 (closed)