Re-add missing metric: rest_client_request_duration_seconds

[arapulido]

What does this PR do?

The metric called rest_client_request_latency_seconds changed its name to rest_client_request_duration_seconds but that was never changed in our integration, so the metric client.http.requests_duration is missing

https://github.com/kubernetes/kubernetes/blob/8ac5d4d6a92d59bba70844fbd6e5de2383a08c96/CHANGELOG/CHANGELOG-1.14.md#deprecated-metrics

Motivation

I am working on updating the Kube Scheduler OOTB dashboard, but I realized that the current one had the HTTP duration histogram widget empty:

https://a.cl.ly/mXuxXrDg

This is because the corresponding metric is not there.

Additional Notes

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 #12636 (b638e35) into master (a221d6b) will increase coverage by 0.00%.
The diff coverage is 100.00%.

Flag	Coverage Δ
kube_scheduler	97.00% <100.00%> (+0.02%)	⬆️

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