feat: custom PR title (#3063)

[muenchdo]

closes #3063

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[codecov]

Codecov Report

Attention: Patch coverage is 50.00000% with 3 lines in your changes missing coverage. Please review.

Project coverage is 51.14%. Comparing base (3a1ee47) to head (4ed8dcb).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
internal/directives/git_pr_opener.go	50.00%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3107      +/-   ##
==========================================
- Coverage   51.14%   51.14%   -0.01%     
==========================================
  Files         283      283              
  Lines       25469    25474       +5     
==========================================
+ Hits        13026    13028       +2     
- Misses      11750    11752       +2     
- Partials      693      694       +1     

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[muenchdo]

@krancour Please let me know your thoughts on testing here. My thinking here is that we can both assume expressions in promotion steps are evaluated properly (likely tested elsewhere), and that if I pass any title to a Git provider's CreatePullRequest, the pull request will be created with the given title.

[krancour]

@muenchdo correct on both counts. 😄

[krancour]

@muenchdo I think if you re-run codegen, this looks g2g.

[krancour]

LGTM

Thanks for this @muenchdo!