[lake] improve logging for lake tiering

[caozhen1937]

Purpose

Linked issue: close #1899

Brief change log

1. Changed LOG.info to LOG.debug for lake snapshot info
   File: TieringSplitGenerator.java
   Changed the log level from info to debug for the message "Last committed lake table snapshot info is:{}" to reduce verbose logging

2. Added logging for reader-split assignments
   File: TieringSourceEnumerator.java
   Added logging to show which reader is being assigned which split.

3. Added commit status logging in commit operator
   File: TieringCommitOperator.java
   Added multiple logging statements to track commit progress:

• Log when starting a commit
• Log when a commit is successful or skipped
• Log when notifying the coordinator
• Log when committing to lake storage
• Log when committing to Fluss
• Enhanced error logging with table ID context

Tests

API and Format

Documentation