Export k8s flags

[marctc]

This PR moves kubernetes flags to its own exported package.
This is necessary for alloy to enable or disable k8s monitoring.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 71.42857% with 2 lines in your changes missing coverage. Please review.

Project coverage is 81.44%. Comparing base (61c142d) to head (058afb1).
Report is 104 commits behind head on main.

Files with missing lines	Patch %	Lines
pkg/internal/kube/informer_provider.go	71.42%	2 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1038   +/-   ##
=======================================
  Coverage   81.44%   81.44%           
=======================================
  Files         137      137           
  Lines       10962    10962           
=======================================
  Hits         8928     8928           
- Misses       1519     1520    +1     
+ Partials      515      514    -1     

Flag	Coverage Δ
integration-test	56.17% <28.57%> (-0.06%)	⬇️
k8s-integration-test	58.95% <57.14%> (+0.02%)	⬆️
oats-test	37.22% <28.57%> (ø)
unittests	50.93% <28.57%> (ø)

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