[EPIC] add Lance REST Service supports

### Describe the proposal

This issue tracks the development of a Lance REST service. It should follow the Lance Namespace Spec (https://lancedb.github.io/lance/format/namespace/) and support configuring different namespace implementations as backends.

### Task list

see below

Start by reading the Lance Namespace Spec linked in the proposal and inspect how Gravitino currently structures namespace implementations. Define the REST service scope and its configurable namespace backends, then verify support against the specification. The task list is not included, so the completion criteria need clarification.

Written by the indexing model from the issue text.