Fix auto-discovery for latest versions on Kubernetes

[L3n41c]

What does this PR do?

Leverages the possible_prometheus_urls parameter introduced by #9573 in the auto-discovery configuration file.

Motivation

Make the agent able to automatically monitor the Kube API server on most recent versions of Kubernetes without requiring too much user setup.
The goad is to simplify the Kubernetes control plane monitoring setup described in DataDog/documentation#10828.

Additional Notes

Depending on the Kubernetes distribution, the API server can listen on two different default ports: 8443 and 6443.
We need to try both in the auto-discovery configuration.

Review checklist (to be filled by reviewers)

• Feature or bugfix MUST have appropriate tests (unit, integration, e2e)
• PR title must be written as a CHANGELOG entry (see why)
• Files changes must correspond to the primary purpose of the PR as described in the title (small unrelated changes should have their own PR)
• PR must have changelog/ and integration/ labels attached

[codecov]

Codecov Report

Merging #9577 (acb4edb) into master (e97eb15) will not change coverage.
The diff coverage is n/a.

Flag	Coverage Δ
kube_apiserver_metrics	97.35% <ø> (ø)

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