Fix auto-discovery for latest versions on Kubernetes

[L3n41c]

What does this PR do?

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

Motivation

The goad is to simplify the Kubernetes control plane monitoring setup described in DataDog/documentation#10828.

Additional Notes

On older versions of Kubernetes, the etcd metrics were available at http://%%host%%:2379/metrics where %%host%% is the node IP.
On most recent version of Kubernetes, the etcd port is exposed only on secure https endpoint and requires ssl client certificate for authentication.

Whereas a client can decide to ignore a server certificate validation, a client has (thankfully) no way to ask the server to ignore client certificate validation.

That’s why the client ssl certificates needed to talk to etcd will need to be mounted from the host as described in DataDog/documentation#10828.

For etcd, there’s unfortunately no way to make integration work out-of-the-box without any user 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 #9578 (225faa1) into master (e97eb15) will not change coverage.
The diff coverage is n/a.

Flag	Coverage Δ
etcd	93.09% <ø> (ø)

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