[Improvement] Iceberg REST server supports dynamic config for metalake

### What would you like to be improved?

Currently, IRCS can automatically proxy a Gravitino Iceberg catalog under a metalake, but the metalake config is static, which means that every time a new metalake is created, a new IRCS needs to be started. I think the metalake config should also be dynamically fetched from Gravitino

### How should we improve?

_No response_

Start by locating the Iceberg REST server (IRCS) code and its static metalake configuration, then trace how it proxies a Gravitino Iceberg catalog. Clarify the dynamic-fetching behavior for newly created metalakes and verify that the server can proxy them without being restarted.

Written by the indexing model from the issue text.