NIFI-12675: Fixed bug that caused custom Relationships not to work on…

[markap14]

… Python Processors. Added unit test to verify. Also addressed issue in PythonControllerInteractionIT where it did not wait for Processors to become valid (originally this wasn't necessary but when we refactored Processors to initialize in the background this was overlooked).

Summary

NIFI-00000

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  • JDK 21

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[exceptionfactory]

Thanks for the fix and test improvements @markap14, this looks good! +1 merging