Add metrics for scan server reservation write out time and collisions

[DomGarguilo]

Fixes #4509

This PR adds two new metrics:

1. accumulo.scan.reservation.writeout.timer which records the amount of time it takes for reservations to be added to the metadata table
2. accumulo.scan.reservation.collision.count which adds a FunctionCounter that gets incremented if a scan is held up waiting for files that are in flux

I also renamed accumulo.scan.reservation.timer to accumulo.scan.reservation.total.timer.

I have observed the writeout timer and total timer displayed in the metrics via logging:

METRICS: 2024-05-09T14:40:40,149, accumulo.scan.reservation.total.timer{host=localhost,instance.name=uno,port=9996,process.name=sserver,resource.group=default} throughput=1.666667/s mean=0.003309524s max=0.159866629s
METRICS: 2024-05-09T14:40:40,149, accumulo.scan.reservation.writeout.timer{host=localhost,instance.name=uno,port=9996,process.name=sserver,resource.group=default} throughput=0.033333/s mean=0.000017287s max=0.000017287s

I have not observed either the existing busy timeout counter or the new collision counter. If anyone has an ideas on how those might be able to be tested that would be helpful.

[DomGarguilo]

Closing as superseded by #4577