Polaris Iceberg rest catalog backed by HMS

### Is your feature request related to a problem? Please describe.

I understand full iceberg rest catalog support (including writes) is on the way.
Is it possible to set a pluggable backend for the catalog (Eg:- like using Hive Metastore for the iceberg rest catalog)?
Something like what can be done with Gravitino or the Tabular iceberg rest images?

A use case would be to reuse an existing Hive Metastore catalog for Iceberg by adding the Polaris Catalog iceberg rest layer in front so that we can switch our compute and query engines to Unity w/ iceberg rest and at the same time legacy apps can directly interface with HMS

Thanks!

### Describe the solution you'd like

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### Describe alternatives you've considered

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### Additional context

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The issue names no implementation files, tests, or entry points. Start by clarifying the proposed pluggable Hive Metastore backend and its compatibility requirements with the Iceberg REST catalog, then define tests for REST access, existing HMS-backed catalogs, and legacy application access as the completion criteria.

Written by the indexing model from the issue text.