Streamline [JenkinsCoverage] support

[PyvesB]

We support four different Jenkins Coverage plugins. This adds code complexity, the corresponding tests have a tendency to break easily (#10372, #10217, #11736, #9918, etc.), and having all these different flavours contributes to users being confused (#11689, #11794). There's an opportunity to reduce our maintenance burden here.

• The first version of the Code Coverage API is deprecated (this is what we previously called apiv1), and I found no usages of it across Github.
• The Cobertura plugin has reached end of life. None of the usages I looked at seem to work.
• The JaCoCo plugin has reached end of life. Some usages of it still seem to work, but I'd argue Jenkins instances that still run this plugin should really update given it was deprecated in 2024. We're not contributing to a sain ecosystem by supporting EOL software forever.

We're left with the official Coverage Plugin which has replaced all of the above (this is what we previously called apiv4). I've introduced a redirector that maps all the jacoco|cobertura|apiv1|apiv4 routes to a new unique simplified route. Whenever a Jenkins instance updates to the new version of the plugin, this means whatever badge were using were start working again transparently, without them having to update the path.

[github-actions]

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📖	✨ Thanks for your contribution to Shields, @PyvesB!

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[stomde]

@stomde

[stomde]

Ok

[PyvesB]

@stomde you're leaving unhelpful messages on a bunch of random PRs. Could you please clarify your intent?

[stomde]

Copilot issue