[SnapshotV2] Add timestamp of last successful fetch of pinned timestamps in node stats

[ltaragi]

Is your feature request related to a problem? Please describe

We can add the timestamp for the last successful fetch of pinned timestamps to the node stats. This can help in identifying any lags in the fetching process.

Describe the solution you'd like

• RemoteStorePinnedTimestampService has a static method getPinnedTimestamps(). The first value of the returned tuple is when the last fetch of pinned timestamps is triggered . This is the timestamp we need to add to node stats.
• We want to ensure backward compatibility with version checks and check that cluster.remote_store.pinned_timestamps.enabled setting is set as true
• Since we currently don't have a remote store specific metric in the node stats, we can create a new metric class and add this timestamp there

Related component

Storage:Snapshots

Describe alternatives you've considered

No response

Additional context

No response