Add ITKPythonPackage checkout step

[tbirdso]

Current behavior

Build scripts from https://github.com/InsightSoftwareConsortium/ITKPythonPackage are packaged alongside ITK build artifacts in ITKPythonBuilds. This provides insight into the state of the build process at the time of artifact creation. However, steps to build ITK modules against the provided artifacts sometimes require patches for issues that cannot be identified until the builds have been created and released.

Requested behavior

Allow the user to provide a specific ITKPythonPackage commit to designate the build scripts that should be used for creating module wheels. The default ITKPythonPackage tag in the reusable workflow will point towards the latest "stable" commit for building Python wheels for ITK modules and can be updated as patches are merged into the repo.

[tbirdso]

Currently addressed in Windows pipelines only as critical path for v5.3.0 release. Preferred future steps:

1. Update ITKPythonPackage download scripts for each of Windows, Linux, MacOS platforms to perform a checkout step in ITKPythonBuilds archive to get fixed version of build scripts. Requires ITKPythonPackage git tag to be passed in via some exported variable.
2. Continue to fetch download script for requested tag on Linux and MacOS, then export git tag and continue. Update Windows to fetch download script and do the same.

[tbirdso]

Closed in InsightSoftwareConsortium/ITKPythonPackage#232