Register table endpoint should honor access delegation

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

The IRC spec for the register-table endpoint does not mention access delegation headers, contrary to the other table endpoints.

Polaris currently does not consider access delegation at all when registering a table. As a consequence, the returned `LoadTableResult` does not contain any config for vended credentials nor for remote signing.

This is bad, because the returned config is unusable if the client is not in possession of valid credentials to access the storage.

### Describe the solution you'd like

Polaris should honor the access delegation headers in the register-table endpoint, and return appropriate config for either vended credentials or remote signing.

### Describe alternatives you've considered

_No response_

### Additional context

This issue came up while developing support for remote signing:

Some context: https://github.com/apache/polaris/pull/2280#discussion_r2272748983

Start with the register-table endpoint and compare its handling of access delegation headers with the other table endpoints, using the IRC specification and the linked remote-signing discussion for context. Done means the endpoint honors the headers and the returned LoadTableResult contains appropriate vended-credentials or remote-signing configuration.

Written by the indexing model from the issue text.