NIFI-8620: Ensure that we provider appropriate error messages if atte…

[markap14]

…mpting to migrate FlowFiles from one session to another without including full hierarchy; added tests to verify behavior

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Enables X functionality; fixes bug NIFI-YYYY.

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[mattyb149]

Reviewing...

[mattyb149]

+1 LGTM, ran integration test and on a live system. Thanks for the fix! Merging to main