HDDS-11511. Introduce metrics in deletion services of OM

[Tejaskriya]

What changes were proposed in this pull request?

The following metrics are added in OM's deletingServices:
KeyDeleting
No of keys processed for delete in the current iteration and overall since last restart
No of keys sent to scm for delete and response(success/fail) in the current iteration and overall since last restart
Total time spent in current iteration

DirDeleting
No of dirs/empty dirs processed for delete in the current iteration and overall since last restart
No of subfiles processed for delete in the current iteration and overall since last restart
Total time spent in current iteration

Dirpurge
No of dirs purged since last restart and in the last request
No of subfiles purged since last restart and in the last request

Keypurge
No of keys purged since last restart and in the last request

What is the link to the Apache JIRA

https://issues.apache.org/jira/browse/HDDS-11511

How was this patch tested?

Tested manually in docker at the jmx endpoint http://localhost:9874/jmx?qry=Hadoop:service=OzoneManager,name=DeletingServiceMetrics :

{
  "beans" : [ {
    "name" : "Hadoop:service=OzoneManager,name=DeletingServiceMetrics",
    "modelerType" : "DeletingServiceMetrics",
    "tag.Context" : "ozone",
    "tag.Hostname" : "257dd53cacdf",
    "IterationDirDeleted" : 1,
    "IterationDirDuration" : 18,
    "IterationDirRunCount" : 8,
    "IterationDirStartTime" : 515836,
    "IterationFilesMoved" : 0,
    "IterationKeyDuration" : 53,
    "IterationKeyRunCount" : 9,
    "IterationKeyStartTime" : 575834,
    "IterationKeysDeleteSuccess" : 1,
    "IterationKeysDeletionRequest" : 1,
    "IterationKeysProcessed" : 1,
    "IterationSubDirDeleted" : 5,
    "IterationSubDirsMoved" : 1,
    "NumDirDeleted" : 6,
    "NumDirPurged" : 5,
    "NumDirPurgedInLatestRequest" : 5,
    "NumDirsMoved" : 0,
    "NumFilesMoved" : 1,
    "NumKeysDeleteSuccess" : 1,
    "NumKeysDeletionRequest" : 1,
    "NumKeysProcessed" : 1,
    "NumKeysPurged" : 1,
    "NumKeysPurgedInLatestRequest" : 1,
    "NumSubKeysPurged" : 1,
    "NumSubKeysPurgedInLatestRequest" : 1
  } ]
}

[Tejaskriya]

@ashishkumar50 thank you for the reviews, I have addressed the comments, could you please review the update?

[Tejaskriya]

@ashishkumar50 I have addressed all the comments, thank you for the review.
@errose28 could you please review the patch?