[Feature] Add lastCommittedSnapshotId commit metric and document lastScannedSnapshotId scan metric

[junmuz]

Search before asking

• I searched in the issues and found nothing similar.

Motivation

Paimon's commit metrics currently provide detailed information about file counts, sizes, durations, and compaction stats, but they do not expose the snapshot ID produced by each commit. Similarly, the lastScannedSnapshotId scan metric exists in code but is missing from the metrics documentation. Adding these improves observability for operators monitoring streaming ingestion pipelines.

Solution

Add lastCommittedSnapshotId gauge to commit metrics. Document lastScannedSnapshotId and lastCommittedSnapshotId in metrics reference

Anything else?

No response

Are you willing to submit a PR?

• I'm willing to submit a PR!