Support Idempotency-Key in Iceberg REST Catalog API

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

IETF draft: https://datatracker.ietf.org/doc/html/draft-ietf-httpapi-idempotency-key-header-06

Iceberg proposal (author: @huaxingao):
* doc: https://docs.google.com/document/d/1WyiIk08JRe8AjWh63txIP4i2xcIUHYQWFrF_1CCS3uw/edit?tab=t.0#heading=h.jfecktgonj1i
* email: https://lists.apache.org/thread/y91scqfd1g3yd0owbgzrr1d2hm3w78gy

### Describe the solution you'd like

Polaris proposal (author: @huaxingao):
* doc: https://docs.google.com/document/d/1L5A8Cspugsk1dW4Ij4dy5wB5FKa8KnaXT0LHBJdgq9w/edit?tab=t.0
* email: https://lists.apache.org/thread/3n26zfs31oqs8f85st4j7dq7c5sy47h8

### Describe alternatives you've considered

See email discussions.

### Additional context

_No response_

Read the linked IETF Idempotency-Key draft and the Iceberg and Polaris proposal documents first, then inspect the REST Catalog API entry points. Use the proposal and email discussions to establish the expected behavior and acceptance criteria; done means the agreed Idempotency-Key support is implemented consistently across the API.

Written by the indexing model from the issue text.