Document PerfIO S3 client configuration - #15943

Related to #15919.

Description

The PerfIO S3 reader supports selecting Netty or CRT with the existing
spark.rapids.perfio.s3.httpClient setting, but that setting was omitted from the generated
advanced configuration documentation. The Iceberg S3 async tuning settings are specific to
PerfIO and should not be declared as core RapidsConf entries.

This change:

• documents the existing PerfIO S3 HTTP client backend selector, including its supported values
  and default;
• documents the Iceberg S3 response-progress timeout and the optional total-call hard cap. The
  total-call limit is disabled by default because it spans the complete streaming body and can
  abort a healthy but slow transfer; and
• removes the PerfIO-only Iceberg S3 declarations from the core configuration registry while
  retaining their generated user documentation.

The response-progress timeout is the default protection against stalled streaming range reads.
Operators who require an absolute wall-clock bound can opt in with
spark.rapids.iceberg.s3.async.api-call-timeout-ms.

Validation:

• ./build/buildall --clean --profile=350 --module=dist --parallel=64 --option='-DskipTests'
• git diff --check

Performance testing is not required because this change only updates configuration metadata and
documentation; it does not alter request execution.

AI assistance: the implementation and validation were performed with Codex assistance and
reviewed by the author before publication.

Checklists

Documentation

• Updated for new or modified user-facing features or behaviors
• No user-facing change

Testing

• Added or modified tests to cover new code paths
• Covered by existing tests
  (Please provide the names of the existing tests in the PR description.)
• Not required

Performance

• Tests ran and results are added in the PR description
• Issue filed with a link in the PR description
• Not required