NIFI-9382: Created a new ClassloaderIsolationKey mechanism by which H…

[markap14]

…adoop related processors (and potentially others) can indicate that they need full classloaders to be cloned but can share with other instances in certain circumstances

• Added system tests

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[adenes]

Thanks @markap14 for the change, it definitely makes sense and the approach looks good to me.
Unfortunately right now I don't have capacity to test the functionality. Reading through the PR I had one comment about the name of the ClassloaderIsolationKey interface.

[bbende]

Latest updates look good, been running a couple of flows concurrently with different principals and is functioning as expected, going to merge