clear dynamic configuration e2e tests

[ElvinEfendi]

What this PR does / why we need it:
Remove redundant/weak tests and extract out some repeating logic. I've also changed the way we detect reload - now the tests are dumping Nginx configuration before and after and comparing the two config.

There's more room to improve but I'll do that in another iteration.

Which issue this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close that issue when PR gets merged): fixes #

Special notes for your reviewer:

[codecov-io]

Codecov Report

Merging #2979 into master will decrease coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #2979      +/-   ##
==========================================
- Coverage   47.54%   47.52%   -0.02%     
==========================================
  Files          77       77              
  Lines        5639     5639              
==========================================
- Hits         2681     2680       -1     
- Misses       2605     2607       +2     
+ Partials      353      352       -1

Impacted Files	Coverage Δ
internal/watch/file_watcher.go	80.76% <0%> (-3.85%)	⬇️

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[ElvinEfendi]

/assign @aledbf

[aledbf]

/lgtm

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: aledbf, ElvinEfendi

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