NIFI-8409 - ConsumeMQTT Processor Broker URI Expression Language Support

[pvillard31]

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Enables X functionality; fixes bug NIFI-YYYY.

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[exceptionfactory]

@pvillard31 Although the PropertyDescriptor definitions are updated, is it also necessary to update the corresponding getProperty() calls to include evaluateExpressionLanguage() in the chain? The associated unit tests also failed during the automated build, although the source of the exception is not clear other than it originating from the onScheduled() method.

[pvillard31]

Thanks @exceptionfactory - updated the pull request

[exceptionfactory]

Thanks for making the updates @pvillard31, looks good!