refactor: replace debugging endpoints integration tests with envtest

[pmalek]

What this PR does / why we need it:

This PR replaces unnecessary integration tests - that test debugging and readiness endpoints of KIC - with envtest based test.

Which issue this PR fixes:

Special notes for your reviewer:

PR Readiness Checklist:

Complete these before marking the PR as ready to review:

• the CHANGELOG.md release notes have been updated to reflect any significant (and particularly user-facing) changes introduced by this PR

[codecov]

Codecov Report

Patch coverage: 92.8% and project coverage change: +0.2 🎉

Comparison is base (d8c1396) 60.1% compared to head (d32c8ca) 60.3%.

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #4094     +/-   ##
=======================================
+ Coverage   60.1%   60.3%   +0.2%     
=======================================
  Files        150     150             
  Lines      16727   16736      +9     
=======================================
+ Hits       10066   10107     +41     
+ Misses      6024    5997     -27     
+ Partials     637     632      -5     

Impacted Files	Coverage Δ
internal/cmd/rootcmd/rootcmd.go	13.8% <0.0%> (ø)
internal/cmd/rootcmd/run.go	36.8% <100.0%> (+15.7%)	⬆️
internal/manager/conditions.go	91.6% <100.0%> (-8.4%)	⬇️
internal/manager/config.go	94.9% <100.0%> (+0.2%)	⬆️

... and 5 files with indirect coverage changes

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[czeslavo]

I like the intention of ripping things that do not really depend on Kong instance out of integration tests suite. I see the value in being able to run tests locally, quickly, and in isolation (sadly cannot say that about integration tests). 👍