Improve startPipeline error handling

[vbanos]

Return error and use panic only once in the controller.

This way its cleaner and it would be easier to use it in tests.

Relevant to: #473

[codecov-commenter]

Codecov Report

❌ Patch coverage is 8.33333% with 22 lines in your changes missing coverage. Please review.
✅ Project coverage is 56.26%. Comparing base (0837f4d) to head (5508747).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
internal/pkg/controler/pipeline.go	9.09%	18 Missing and 2 partials ⚠️
internal/pkg/controler/controler.go	0.00%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #481      +/-   ##
==========================================
- Coverage   56.42%   56.26%   -0.16%     
==========================================
  Files         130      130              
  Lines        8091     8104      +13     
==========================================
- Hits         4565     4560       -5     
- Misses       3161     3177      +16     
- Partials      365      367       +2     

Flag	Coverage Δ
e2etests	40.57% <8.33%> (-0.08%)	⬇️
unittests	29.28% <0.00%> (-0.10%)	⬇️

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[NGTmeaty]

Looks great. Thank you!