Merging app and network K8s informers

[mariomac]

Inherited from our legacy code, we had two kubernetes informers, one for the Application pipeline and another for the Network pipeline.

This PR unifies both, as a performance improvement (less connection to the Kube API), and as a previous step for some required improvements that will be done in the future, such as letting the users to selectively disable some informers (e.g. ReplicaSets for performance reasons) and decorating service names in Service Graph metrics.

[grcevski]

LGTM! Amazing thanks for doing this so quickly!

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 73.64341% with 68 lines in your changes missing coverage. Please review.

Project coverage is 80.27%. Comparing base (657f710) to head (92ad282).

Files	Patch %	Lines
pkg/internal/kube/informer_ip.go	71.81%	24 Missing and 7 partials ⚠️
pkg/internal/kube/informer_provider.go	64.28%	11 Missing and 4 partials ⚠️
pkg/internal/kube/informer.go	70.21%	7 Missing and 7 partials ⚠️
pkg/internal/appolly/appolly.go	57.14%	2 Missing and 1 partial ⚠️
pkg/internal/netolly/transform/k8s/kubernetes.go	85.71%	2 Missing and 1 partial ⚠️
pkg/internal/discover/watcher_kube.go	60.00%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #956      +/-   ##
==========================================
+ Coverage   80.04%   80.27%   +0.22%     
==========================================
  Files         133      134       +1     
  Lines       10522    10477      -45     
==========================================
- Hits         8422     8410      -12     
+ Misses       1581     1561      -20     
+ Partials      519      506      -13     

Flag	Coverage Δ
integration-test	55.98% <12.40%> (+0.30%)	⬆️
k8s-integration-test	58.87% <70.54%> (+0.03%)	⬆️
oats-test	36.18% <9.68%> (+0.25%)	⬆️
unittests	49.00% <23.25%> (+0.51%)	⬆️

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