NIFI-13394: Check candidate virtual env for python command.

[bobpaulin]

Summary

NIFI-13394

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Built and started up on windows with python modules.

Build

• Build completed using mvn clean install -P contrib-check
  • JDK 21

Licensing

• New dependencies are compatible with the Apache License 2.0 according to the License Policy
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Documentation

• Documentation formatting appears as expected in rendered files

[exceptionfactory]

Thanks for working on this @bobpaulin. The concept makes sense, but for null-safety, I recommend reworking the command resolution a bit.

[exceptionfactory]

Thanks for the updates @bobpaulin. The new method looks cleaner, but the unit tests are now failing, so it looks like some additional changes are required.

[exceptionfactory]

Thanks for working through the feedback @bobpaulin, the latest version looks good! +1 merging