fix: Fix cancel in progress to act on same pr/branch

[chmouel]

Changes

We need to ensure that we only cancel the pipeline run that is running
on the same branch as the current PR or push event. This ensures that we
don't cancel the wrong pipeline run.

On PullRequest events, we only cancel the pipeline run that is running
on the same Pull Request number.

On Push events, we only cancel the pipeline run that is running on the
same SourceBranch (which is the same as HeadBranch on push)

This avoids the issue when you have multiple pull request running on a
repo and we don't cancel the wrong ones that are running for a different
PR.

Tried to do e2e tests but it ended too flaky.

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[chmouel]

I have a new laptop and the setup create pr against origin instead of my fork, should be fixed for next pr

[codecov]

Codecov Report

Attention: Patch coverage is 83.33333% with 4 lines in your changes missing coverage. Please review.

Project coverage is 65.34%. Comparing base (eb50fac) to head (bb7375f).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
pkg/pipelineascode/cancel_pipelineruns.go	83.33%	3 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1826      +/-   ##
==========================================
+ Coverage   65.28%   65.34%   +0.06%     
==========================================
  Files         177      177              
  Lines       13674    13692      +18     
==========================================
+ Hits         8927     8947      +20     
  Misses       4143     4143              
+ Partials      604      602       -2     

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[chmouel]

copyng a comment i made offline on a slack discussion:

maybe in the future we would need to have concurrency groups to let the user choose their groupping
that may come up whenever we integrate that feature in a new concurrency abstracted from pac controller (ie: the far future)
but i think the way that pr implemented the grouping is good and conservative enough for the most common use case 

[chmouel]

fixed the e2e-tests and made it to test over over multiple pull request, rephrased documentation to make it clear how the cancellation selection works.