WIP: enabling external informer

[mariomac]

This function enables a new configuration option that allows switching from the local Kube API informer client to a gRPC stream client that connects to the external beyla-k8s-cache service.

Missing:

• Unit tests
• Integration tests
• Creating the Docker image of the beyla-k8s-cache (ticket opened)

There are some TO-DOs that will be left for future PRs, as this feature will still remain officially unreleased and hidden from the documentation.

This PR also fixes a bug: if Beyla was running with host network, the host.id was not properly retrieved.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 81.94444% with 13 lines in your changes missing coverage. Please review.

Project coverage is 80.57%. Comparing base (ca5f23e) to head (11eb6ef).

Files with missing lines	Patch %	Lines
pkg/internal/kube/cache_svc_client.go	82.35%	8 Missing and 1 partial ⚠️
pkg/internal/kube/informer_provider.go	82.35%	3 Missing ⚠️
pkg/internal/pipe/global/host_id.go	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1266      +/-   ##
==========================================
+ Coverage   80.42%   80.57%   +0.15%     
==========================================
  Files         132      133       +1     
  Lines       13535    13597      +62     
==========================================
+ Hits        10885    10956      +71     
+ Misses       2133     2128       -5     
+ Partials      517      513       -4     

Flag	Coverage Δ
integration-test	60.68% <11.11%> (-0.17%)	⬇️
k8s-integration-test	57.63% <76.38%> (+0.48%)	⬆️
oats-test	36.23% <1.38%> (-0.16%)	⬇️
unittests	52.78% <2.77%> (-0.28%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.