internal instrumentation for k8s cache

[mariomac]

Will provide a view of how much load is the k8s cache carrying out.

Done:

• Integration tests.
• Modify helm chart.

[codecov]

Codecov Report

Attention: Patch coverage is 91.04478% with 12 lines in your changes missing coverage. Please review.

Project coverage is 78.46%. Comparing base (e766187) to head (5e863de).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
pkg/kubecache/meta/informers_init.go	64.28%	0 Missing and 5 partials ⚠️
pkg/kubecache/instrument/imetrics.go	95.50%	4 Missing ⚠️
pkg/kubecache/instrument/server.go	82.35%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1365      +/-   ##
==========================================
+ Coverage   78.35%   78.46%   +0.11%     
==========================================
  Files         145      147       +2     
  Lines       14639    14762     +123     
==========================================
+ Hits        11470    11583     +113     
- Misses       2570     2576       +6     
- Partials      599      603       +4     

Flag	Coverage Δ
k8s-integration-test	59.84% <83.58%> (+0.24%)	⬆️
oats-test	34.18% <0.00%> (-0.17%)	⬇️
unittests	51.84% <22.38%> (-0.31%)	⬇️

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