feat(controller)!: assign a default alias to promotion steps that have none

[krancour]

Part of #2845

This PR make the step execution engine assign a default alias to any promotion step that doesn't explicitly have an alias specified.

This makes it such that all steps leave behind outputs in the shared state map where that was only possible before for steps that had explicitly been assigned an alias.

This creates the possibility of modifying some step implementations, in a follow-up, to consult any output they themselves may have produced in a previous execution.

This is braking only insofar as it reserves step aliases of the form ^step-\d+$ for system use.

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[hiddeco]

Maybe better to make this publicly accessible and have the webhook depend on it?

[krancour]

I didn't want to make the webhook dependent on this package or vice versa, but since you've called me out on this, I probably should move this to api/v1alpha1. Pretty much everything already depends on that and that is arguably a better location for this anyway.

Fix incoming.

[krancour]

Fixed in 185a14f

[codecov]

Codecov Report

Attention: Patch coverage is 70.58824% with 10 lines in your changes missing coverage. Please review.

Project coverage is 50.01%. Comparing base (f30f66b) to head (185a14f).
Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
internal/directives/simple_engine.go	28.57%	9 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2881      +/-   ##
==========================================
+ Coverage   49.95%   50.01%   +0.05%     
==========================================
  Files         275      275              
  Lines       24493    24556      +63     
==========================================
+ Hits        12236    12282      +46     
- Misses      11587    11603      +16     
- Partials      670      671       +1     

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