[NIFI-15162] Flow metrics reporting strategy for nifi metrics api

[esecules]

Summary

NIFI-15162
This reintroduces the metrics reporting strategy feature from the PrometheusReportingTask. It can be used to only collect flow metrics related to process groups. This will help reduce the CPU load of collection metrics from larger flows when the flow admin wants to omit individual processor and connection metrics already.

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• Apache NiFi Jira issue created

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Build

• Build completed using ./mvnw clean install -P contrib-check
  • JDK 21
  • JDK 25

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[exceptionfactory]

Thanks for working on this improvement @esecules.

The change looks straightforward, I noted a few implementation recommendations.

[esecules]

@exceptionfactory would you like me to squash the 3 commits here into 1 or are we good?

[exceptionfactory]

@exceptionfactory would you like me to squash the 3 commits here into 1 or are we good?

Thanks for asking, no need to squash commits during the review, I can do it when ready on merge.

[exceptionfactory]

Thanks for updates @esecules! This looks close to completion, but I noted where the updated method argument appears to require updating references in the method to change the value comparison, then this should be ready to go forward.

[esecules]

Good catch on the equality check @exceptionfactory! I've made the changes and also noticed i could simplify the enum definition for the reporting strategy since we don't make use of the descriptions anywhere since its not a parameter in the UI anymore like it was in the reporting task.

[esecules]

I checked the two failing system tests and they both pass on my macbook using java 21 and 25 according to each test failure.

[exceptionfactory]

Thanks for the simplified enum approach @esecules, that looks good. I noted one more minor adjustment for equals checking of the enum values, then this should be ready to go.

[exceptionfactory]

Thanks for the work on this @esecules! +1 merging