chore(controller): make backoff configurable for tests

[hiddeco]

Primarily to be able to overwrite it in tests, as the previous approach caused an unnecessary delay for the unit tests.

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[codecov]

Codecov Report

Attention: Patch coverage is 12.50000% with 7 lines in your changes missing coverage. Please review.

Project coverage is 51.20%. Comparing base (0b548db) to head (d89d93f).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
internal/controller/stages/regular_stages.go	12.50%	7 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3074      +/-   ##
==========================================
- Coverage   51.23%   51.20%   -0.03%     
==========================================
  Files         283      283              
  Lines       25465    25466       +1     
==========================================
- Hits        13047    13041       -6     
- Misses      11722    11729       +7     
  Partials      696      696              

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[krancour]

Very nice improvement!