HDDS-14960. OM Web UI dashboard for Ozone Snapshot

[jojochuang]

What changes were proposed in this pull request?

HDDS-14960. OM Web UI dashboard for Ozone Snapshot

Please describe your PR in detail:

• Create a Ozone Snapshot dashboard tab in OM Web UI, that displays:

1. Usage statstics – number of active, deleted snapshots, size of current snapshot cache.
2. List of snapshot diff jobs – status text, progress, creation time; search&sort capabilities.
3. Snapshot internal metrics in OmSnapshotInternalMetrics.

The implementation includes:

1. Frontend code to display usage statistics, snapshot diff jobs, internal metrics, code to support search and sort capabilities.
2. Backend code: SnapshotDiffManager implements SnapshotDiffManagerMXBean and register it with the runtime.
3. Test code to ensure the MXBean is registered correctly, and the values is expected.

SnapshotDiffJob getCodec() renamed to codec() to avoid clashes with JMXBean conventions.

Gemini CLI model gemini-3-flash-preview

What is the link to the Apache JIRA

https://issues.apache.org/jira/browse/HDDS-14960

How was this patch tested?

Unit tests, manually inspected frontend web UI after executing this command (screen shot attached)

ozone sh volume create vol1
ozone sh bucket create vol1/bucket1
ozone sh snapshot create vol1/bucket1 snap1
ozone sh key put vol1/bucket1/key1 /etc/krb5.conf
ozone sh snapshot create vol1/bucket1 snap2
ozone sh snapshot diff vol1/bucket1 snap1 snap2
ozone sh snapshot lsDiff vol1/bucket1 -a
ozone sh key delete vol1/bucket1/key1
ozone sh snapshot create vol1/bucket1 snap3
ozone sh snapshot diff vol1/bucket1 snap2 snap3
ozone sh snapshot diff vol1/bucket1 snap1 snap3
ozone sh snapshot lsDiff vol1/bucket1 -a```