NIFI-16256 Deprecate AbstractPolicyBasedAuthorizer for removal

[exceptionfactory]

Summary

NIFI-16256 Deprecates the AbstractPolicyBasedAuthorizer for removal in subsequent minor release versions.

The abstract Authorizer has no functional implementation within the project. Changes include removing the MockPolicyBasedAuthorizer and associated nifi-mock-authorizer module, which were limited to testing.

These changes follow the approval of NIP-39 and prepare for the transition away from fine-grained authorization.

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