test(e2e): use builder for regexes

[phm07]

This PR introduces a new builder for regular expressions, which makes tests easier to understand and maintain.

[codecov]

Codecov Report

Attention: Patch coverage is 96.66667% with 2 lines in your changes missing coverage. Please review.

Project coverage is 71.63%. Comparing base (120aa03) to head (8413f66).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
test/e2e/util.go	96.66%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #872      +/-   ##
==========================================
+ Coverage   71.45%   71.63%   +0.17%     
==========================================
  Files         243      244       +1     
  Lines        8731     8791      +60     
==========================================
+ Hits         6239     6297      +58     
- Misses       1824     1826       +2     
  Partials      668      668              

Flag	Coverage Δ
e2e	44.28% <96.66%> (+0.37%)	⬆️
unit	65.96% <0.00%> (-0.46%)	⬇️

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