MINIFICPP-2746 Allow python processors to run in parallel

[lordgamez]

https://issues.apache.org/jira/browse/MINIFICPP-2746

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[szaszm]

Suggested change

One feature that is currently only available in MiNiFi C++ is the ability to set a python processor to be single threaded. This is not yet available in NiFi's API, but similarly to Nifi's `@TriggerSerially` annotation, in MiNiFi C++ the `@trigger_serially` decorator can be used to make a processor single threaded. Setting this will make sure that only one thread executes the processor, and setting the max concurrent tasks to more than 1 in the flow configuration will not have any effect.

One feature that is currently only available in MiNiFi C++ is the ability to set a python processor to be single threaded. This is not yet available in NiFi's Python API, but similarly to Nifi's `@TriggerSerially` Java API annotation, in MiNiFi C++ the `@trigger_serially` decorator can be used to make a processor single threaded. Setting this will make sure that only one thread executes the processor, and setting the max concurrent tasks to more than 1 in the flow configuration will not have any effect.