HDDS-15446. Expose Hard Min Free Space Threshold via JMX

[anuragp010]

What changes were proposed in this pull request?

The hard minimum free space threshold is not available via JMX on Datanodes. The write path rejection logic uses the hard threshold, which is exposed through the getFreeSpaceToSpare method on HddsVolume. This PR exposes the metric in JMX.

What is the link to the Apache JIRA

HDDS-15446

How was this patch tested?

1. Unit test was updated.
2. Tested Manually:

bash-5.1$ curl -XGET http://ozone-datanode-1:9882/jmx?qry=Hadoop:service=HddsDatanode,name=VolumeInfoMetrics-/data/hdds
{
  "beans" : [ {
    "name" : "Hadoop:service=HddsDatanode,name=VolumeInfoMetrics-/data/hdds",
    "modelerType" : "VolumeInfoMetrics-/data/hdds",
    "tag.Context" : "ozone",
    "tag.DatanodeUuid" : "5fa333c2-71a4-43bc-b95f-968a925cefa6",
    "tag.StorageType" : "DISK",
    "tag.VolumeType" : "DATA_VOLUME",
    "tag.StorageDirectory" : "/data/hdds/hdds",
    "tag.VolumeState" : "NORMAL",
    "tag.Hostname" : "3319dfbfbcbf",
    "AvailableSpaceInsufficient" : 0,
    "DbCompactLatencyNumOps" : 0,
    "DbCompactLatencyAvgTime" : 0.0,
    "NumContainerCreateRequestsInSoftBandMinFreeSpace" : 0,
    "NumContainerCreateRequestsRejectedHardMinFreeSpace" : 0,
    "NumScans" : 1,
    "NumScansSkipped" : 0,
    "NumWriteRequestsInSoftBandMinFreeSpace" : 0,
    "NumWriteRequestsRejectedHardMinFreeSpace" : 0,
    "ReservedCrossesLimit" : 1,
    "Committed" : 0,
    "LayoutVersion" : 1,
    "Containers" : 0,
    "OzoneCapacity" : 105076655700,
    "OzoneAvailable" : 91655196672,
    "OzoneUsed" : 4382720,
    "Reserved" : 10508716,
    "FilesystemCapacity" : 105087164416,
    "FilesystemAvailable" : 91655196672,
    "FilesystemUsed" : 13431967744,
    "MinFreeSpace" : 104857600,
    "HardMinFreeSpace" : 104857600,
    "NonOzoneUsed" : 13427585024
  } ]
}bash-5.1$

3. DN UI shows the new metric:

[priyeshkaratha]

Thanks @anuragp010 for the patch and changes LGTM

[priyeshkaratha]

@devmadhuu Can you review the changes?