[Matrix-Generation] Support additional customized steps before matrix generation

[scbedd]

@benbp

This extension will allow the python regression testing to dynamically update it's matrix.

Related to Azure/azure-sdk-for-python#23519

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[azure-sdk]

The following pipelines have been queued for testing:
java - template
java - template - tests
js - template
net - template
net - template - tests
python - template
python - template - tests
You can sign off on the approval gate to test the release stage of each pipeline.
See eng/common workflow

[scbedd]

Well I was going to post a comment with a "all done" confirming that this works...and it doesn't.

Build
Commit

Currently debugging before continuing with the common update.

[azure-sdk]

The following pipelines have been queued for testing:
java - template
java - template - tests
js - template
net - template
net - template - tests
python - template
python - template - tests
You can sign off on the approval gate to test the release stage of each pipeline.
See eng/common workflow

[scbedd]

After steplist update, checks out.

Advancing this to merge.

[azure-sdk]

The following pipelines have been queued for testing:
java - template
java - template - tests
js - template
net - template
net - template - tests
python - template
python - template - tests
You can sign off on the approval gate to test the release stage of each pipeline.
See eng/common workflow

[azure-sdk]

The following pipelines have been queued for testing:
java - template
java - template - tests
js - template
net - template
net - template - tests
python - template
python - template - tests
You can sign off on the approval gate to test the release stage of each pipeline.
See eng/common workflow

[scbedd]

I want to squash this set of commits down, but have already pushed the results (and squashed) to each destination repo. Going to check-enforcer override, then merge this build manually to get the commit history I want.

Next time I'll avoid the situation entirely.

[scbedd]

/check-enforcer override