[FEATURE] Support dynamic metalake config for Iceberg REST server

### Describe the feature

Iceberg REST server fetch catalog only under one metalake, metalake config is static configured in conf file for now.
REST APIs should support metalake in the request uri path.

### Motivation

_No response_

### Describe the solution

_No response_

### Additional context

_No response_

Start by locating the Iceberg REST server request-routing entry points and the current static metalake configuration. Trace how the metalake is selected for catalog fetches, then verify that request URI paths can provide it and add coverage for the supported REST APIs; done means requests are no longer limited to the configured metalake.

Written by the indexing model from the issue text.