[lake/tiering] Add pendingTime and freshness metrics for lake tiering tables

[beryllw]

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Description

Add two new table-level metrics for lake tiering to improve monitoring capabilities:

1. pendingTime: Tracks how long a table has been waiting in the pending queue for tiering
2. freshness: Exposes the user-configured table data freshness interval in milliseconds

Willingness to contribute

• I'm willing to submit a PR!