Expose JMX metrics for processing speed

[blootsvoets]

There is no reliable way to see how the output generation is performing. We should add metrics to have a better understanding and to monitor this. The following metrics come to mind:

• isProcessing: whether the service is currently executing something
• recordsProcessedCount: how many records are being processed. You can use prometheus with rate to get an insight in what the current processing rate is.
• recordsUnprocessedCount: how many records are currently unprocessed. The baseline for this is only computed at the start of a scan cycle. Probably, this should be baseLineCount - recordsProcessedCountInCurrentBatch.
• recordsProcessedCountInCurrentBatch
• etaInCurrentBatch