HDDS-8746. Add metrics to ReplicationSupervisor for task count and max streams

[sodonnel]

What changes were proposed in this pull request?

To give added visibility into the Replication Queue on a datanode, this Jira adds some extra metrics to give visibility into the count of "normal priority" Replication and Reconstruction tasks, along with the current maxStreams setting, which is automatically adjusted when the node moves into decommission.

What is the link to the Apache JIRA

https://issues.apache.org/jira/browse/HDDS-8746

How was this patch tested?

This was tested manually in Docker compose by sampling the JMX output. Sample output:

    "name" : "Hadoop:service=HddsDatanode,name=ReplicationSupervisorMetrics",
    "modelerType" : "ReplicationSupervisorMetrics",
    "tag.Hostname" : "b297306fcf0f",
    "numInFlightReplications" : 5,
    "numQueuedReplications" : 4,
    "numRequestedReplications" : 1,
    "numTimeoutReplications" : 0,
    "numSkippedReplications" : 0,
    "maxReplicationStreams" : 1, ** newly added
    "numInflightECReconstructionCoordinatorTask" : 5 ** newly added


    "name" : "Hadoop:service=HddsDatanode,name=ReplicationSupervisorMetrics",
    "modelerType" : "ReplicationSupervisorMetrics",
    "tag.Hostname" : "b297306fcf0f",
    "numInFlightReplications" : 1,
    "numQueuedReplications" : 0,
    "numRequestedReplications" : 6,
    "numTimeoutReplications" : 0,
    "numSkippedReplications" : 0,
    "maxReplicationStreams" : 1,      ** newly added
    "numInflightReplicationTask" : 1,  ** newly added
    "numInflightECReconstructionCoordinatorTask" : 0 ** newly added

[adoroszlai]

Thanks @sodonnel for the patch, LGTM.