NIFI-9455 Add aggregated predictions to Prometheus

[timeabarna]

https://issues.apache.org/jira/browse/NIFI-9455

Description of PR

Adding root level aggregated prediction metrics

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[exceptionfactory]

Thanks for the improvements @timeabarna! The filtering parameters are similar to the current PR #5571. Could you take a look at that PR and consider how the changes here would align?

PR #5571 implements similar sample name filtering, and include includes a collector registry filter, it also leverages the existing CollectorRegistry.filteredMetricFamilySamples() method to select one or more sample names. I would like to incorporate those changes to improve filtering for the existing Prometheus producer output before introducing the new JSON producer output if possible, so it would be helpful to get your feedback on that PR before moving forward on this one.

[timeabarna]

This PR is pending on #5673

[timeabarna]

Thanks @exceptionfactory for your help. This PR should be the final of the consolidated PRs, can you please help reviewing it?

[exceptionfactory]

Thanks for updating this pull request and implementing the features @timeabarna. The implementation looks straightforward, just a few small notes regarding the potential for declaring and reusing some static variables.

[timeabarna]

Thanks @exceptionfactory for your review, I've modified the code based on your recommendations.

[exceptionfactory]

Thanks for making the adjustments @timeabarna! The changes look good and work as expected at runtime. +1 Merging.