Add telemetry metrics counter by ksm collector

[clamoriniere]

What does this PR do?

Add additional telemetry metrics to know how many metrics are return in the ksm prometheus payload.
the .telemetry.collector.metrics.count can have two tag keys:

• name: the name of the collector, corresponding to the object type.
• kube_namespace: the kubernetes namespace if the object is namespaced in kube.

Motivation

What inspired you to submit this pull request?

Additional Notes

Anything else we should know when reviewing?

Review checklist (to be filled by reviewers)

• 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
• Feature or bugfix must have tests
• Git history must be clean
• If PR adds a configuration option, it must be added to the configuration file.

[codecov]

Codecov Report

Merging #4125 into master will decrease coverage by 2.01%.
The diff coverage is 81.81%.

@@            Coverage Diff             @@
##           master    #4125      +/-   ##
==========================================
- Coverage   86.55%   84.54%   -2.02%     
==========================================
  Files         744       69     -675     
  Lines       38431     5415   -33016     
  Branches     4639      675    -3964     
==========================================
- Hits        33265     4578   -28687     
+ Misses       3922      683    -3239     
+ Partials     1244      154    -1090

[AlexandreYang]

Few minor comments.

[clamoriniere]

@pierre and @AlexandreYang: PR ready for a new review

[AlexandreYang]

LGTM

[mfpierre]

👍