Fix AWSCRTHTTPClient request bodies for HTTP/1.1 connections

[arandito]

Description

Previously, our AWSCRTHTTPClient attached request bodies via the CRT's request_body_generator parameter, which is only supported for HTTP/2 connections (source). This caused generated clients that only support HTTP/1.1 to throw the following error when making body-bearing requests:

smithy_core.exceptions.SmithyError: 2056 (AWS_ERROR_HTTP_MISSING_BODY_STREAM): Given the provided headers (ex: Content-Length), a body is expected.

This PR adds logic that routes HTTP/1.1 connections to attach bodies through the body_stream parameter on the request itself and keeps the generator path for HTTP/2.

Testing

• Generated H1-only service (STS) and confirmed calls no longer raise AWS_ERROR_HTTP_MISSING_BODY_STREAM
• Confirmed existing client integration tests succeed with changes

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.