Add metrics to measure latency of k8s informer

[marctc]

This can be helpful to measure latency of k8s informers in Beyla and count the total requests to k8s API.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 81.53846% with 12 lines in your changes missing coverage. Please review.

Project coverage is 81.12%. Comparing base (fb456f1) to head (83108e0).

Files with missing lines	Patch %	Lines
pkg/internal/imetrics/imetrics.go	54.54%	5 Missing ⚠️
pkg/internal/imetrics/iprom.go	88.46%	3 Missing ⚠️
pkg/internal/transform/kube/db.go	76.92%	3 Missing ⚠️
pkg/internal/appolly/appolly.go	0.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1200      +/-   ##
==========================================
+ Coverage   81.07%   81.12%   +0.05%     
==========================================
  Files         136      136              
  Lines       11501    11551      +50     
==========================================
+ Hits         9324     9371      +47     
- Misses       1643     1647       +4     
+ Partials      534      533       -1     

Flag	Coverage Δ
integration-test	57.13% <36.92%> (+0.17%)	⬆️
k8s-integration-test	58.99% <81.53%> (+0.23%)	⬆️
oats-test	35.66% <6.15%> (-0.16%)	⬇️
unittests	53.12% <12.30%> (-0.18%)	⬇️

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[mariomac]

LGTM!