[FEATURE] Iceberg Rest: Support of S3 Proxy Host and Port

### Describe the feature

Add support of S3:
- s3.proxy.host
- s3.proxy.port
to the Iceberg Catalog definition, so that a client can also fetch S3 proxy settings along side with already existing properties like endpoint, pathStyleAccess and region.

### Motivation

Allow Catalog Clients like Flink and Spark to use proxy settings to be able to work S3 behind the HTTP PROXY.

### Describe the solution

Add two properties the Iceberg REST Catalog definition so that they can be passed down to S3 HTTP Client.

### Additional context

_No response_

Locate the Iceberg REST Catalog definition and the existing handling for endpoint, pathStyleAccess, and region. Trace how those properties reach the S3 HTTP client, then add equivalent proxy host and port support and verify that catalog clients such as Flink and Spark can receive the settings.

Written by the indexing model from the issue text.