Federation of Catalog-level entities to remote catalogs #540
Description
Is your feature request related to a problem? Please describe.
As Iceberg users sometimes find different Iceberg-catalog sources of truth being created organically over time, it can be difficult to consolidate or centralize workloads onto a new target architecture or onboard new catalog implementations like Polaris to unlock its RBAC features without disrupting ongoing workloads.
Being able to have one Catalog instance serve as a combined "pane of glass" serving the contents of a legacy Catalog alongside new datasets enables an incremental migration or even simply enabling different workloads to leverage different catalog features without a stop-the-world migration.
Describe the solution you'd like
Read-through federation of Catalog entities (e.g. Namespaces, Tables, Views) would allow a Polaris instance to link in an existing remote Catalog as a source-of-truth while exposing a Polaris entry-point along with Polaris RBAC features without performing a disruptive migration of Catalog contents.
Ideally, this federation would require minimal setup of the initial catalog connection while still benefiting from all the fine-grained access control features expected from normal Polaris catalogs; it should intelligently pass through API operations but also allow defining privilege grants on entities without requiring prior setup/syncing of those entities into the Polaris federation layer.
Describe alternatives you've considered
No response
Additional context
No response