[lake/tiering] Add More Tiering Monitoring Metrics

[beryllw]

Search before asking

• I searched in the issues and found nothing similar.

Motivation

Introduce a set of monitoring metrics focused on the tiering process, including file/record sizes, read/write throughput.

Solution

No response

Anything else?

No response

Willingness to contribute

• I'm willing to submit a PR!

[Prajwal-banakar]

"Hi @beryllw , I've analyzed the current implementation.

My implementation plan is to:

Extend WriterInitContext to expose the MetricGroup, allowing lake writers to access the monitoring system.

Instrument RecordWriter to track tieringRecordCount and tieringWriteBytes in the write path.

Capture fileSizeInBytes from the WriteResult in IcebergLakeWriter to monitor the final tiered file sizes.

This approach keeps the metrics logic centralized and consistent with the existing Replica metric hierarchy. I'm ready to work on this issue if this plan looks good to you!