HDDS-8783. Add metrics for volume scanner

[sarvekshayr]

What changes were proposed in this pull request?

Added below listed metrics for volume scanner:

• NumVolumeChecks
• NumAllVolumeChecks
• NumAllVolumeSetsChecks
• NumSkippedChecks

(More metrics can be added further.)

What is the link to the Apache JIRA

HDDS-8783

How was this patch tested?

Checked manually in DN JMX:
http://localhost:57859/jmx?qry=Hadoop:service=HddsDatanode,name=StorageVolumeCheckerMetrics

{
  "beans" : [ {
    "name" : "Hadoop:service=HddsDatanode,name=StorageVolumeCheckerMetrics",
    "modelerType" : "StorageVolumeCheckerMetrics",
    "tag.Context" : "dfs",
    "tag.Hostname" : "fd2d58b52937",
    "NumAllVolumeChecks" : 2,
    "NumAllVolumeSetsChecks" : 0,
    "NumSkippedChecks" : 0,
    "NumVolumeChecks" : 0
  } ]
}

after an hour volume scanner runs again

{
  "beans" : [ {
    "name" : "Hadoop:service=HddsDatanode,name=StorageVolumeCheckerMetrics",
    "modelerType" : "StorageVolumeCheckerMetrics",
    "tag.Context" : "dfs",
    "tag.Hostname" : "fd2d58b52937",
    "NumAllVolumeChecks" : 4,
    "NumAllVolumeSetsChecks" : 1,
    "NumSkippedChecks" : 0,
    "NumVolumeChecks" : 0
  } ]
}