[PROPOSAL] Change kahadb stats to be microseconds in 5.17.x

[Matt Pavlovich]

Currently, KahaDB stats are in ms and we get invalid rollup values for minTime, 
averageTime, and totalTime, since a large number of operations take < 1ms on 
modern hardware. I propose we convert the units to be microseconds to provide 
better granularity and correctness. I have created a JIRA to track this change: 
https://issues.apache.org/jira/browse/AMQ-8414 
<https://issues.apache.org/jira/browse/AMQ-8414>

For comparison, Apache CXF also uses microseconds for metrics for service 
operations.

Sample:
Broker uptimeMillis: 835951271 <-- 9 days
KahaDB  "totalTime": 62568920797,  <-- 724.177324039352 days


{
  "writeTime": {
    "maxTime": 5812,
    "averageTime": 16.418624299081607,
    "minTime": 0,
    "totalTime": 62568920797,
    "count": 3810850389,
    "averagePerSecond": 60.906442694832606,
    "averagePerSecondExMinMax": 60.9064483204415,
    "averageTimeExMinMax": 16.418622782579472
  },
  "readTime": {
    "maxTime": 517,
    "averageTime": 0.27722760803497465,
    "minTime": 0,
    "totalTime": 264011084,
    "count": 952326090,
    "averagePerSecond": 3607.144350045546,
    "averagePerSecondExMinMax": 3607.1514061783746,
    "averageTimeExMinMax": 0.2772270657359121
  }
}

Thanks,
Matt Pavlovich