[FEATURE REQUEST] External catalog via REST delegation

[jkolash]

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

I would like to ideally only configure 1 endpoint for all of my iceberg catalog readers and delegate through polaris.

Describe the solution you'd like

I would like to be able to support external catalog delegating via rest endpoints. This would allow all external iceberg catalog locations to be managed in polaris but not have to directly integrate with multiple catalog endpoints client side.

Once an external catalog rest endpoint location is added to the polaris catalog, any existing integrations immediately are able to read that data if they have permission to do so. It may be possible to simply forward exiting oauth credentials or give polaris new credentials to use to talk to the external catalog.

Describe alternatives you've considered

In spark for example you'd need to individually register each catalog endpoint namespace config among multiple clients or code bases. Doing it once on the polaris catalog would simplify integration.

Additional context

No response