add client configuration for aws-chunked encoding buffer size

[sbiscigl]

Description of changes:

Adds a client configuration for the buffer that is used to encode aws-chunked content encoded messages. This is extremely useful when running in a memory restricted enviornment and this needs to be smaller than the default 64KiB

example usage

#include <aws/core/Aws.h>
#include <aws/s3/S3Client.h>
#include <aws/s3/model/PutObjectRequest.h>

#include <fstream>

using namespace Aws;
using namespace Aws::S3;
using namespace Aws::S3::Model;
using namespace Aws::Utils;
using namespace Aws::Utils::Logging;

class sdk_context_context {
 public:
  sdk_context_context(SDKOptions&& options) : options_{std::move(options)} {
    InitAPI(options_);
  }
  ~sdk_context_context() { ShutdownAPI(options_); }

 private:
  SDKOptions options_;
};

auto main() -> int {
  SDKOptions options{};
  options.loggingOptions.logLevel = LogLevel::Debug;
  sdk_context_context context{std::move(options)};

  S3ClientConfiguration configuration{};
  // set to 12 KiB
  configuration.awsChunkedBufferSize = 1024 * 12;
  const S3Client client{configuration};
  auto request = PutObjectRequest{}
                     .WithBucket("bucket")
                     .WithKey("key");
  request.SetBody(Aws::MakeShared<Aws::FStream>(
      "allocation-tag",
      "/some/file/path",
      std::ios_base::in | std::ios_base::out));
  const auto result = client.PutObject(request);
  if (!result.IsSuccess()) {
    std::cout << "Failed to upload file: " << result.GetError().GetMessage()
              << std::endl;
  }
  return 0;
}

Check all that applies:

• Did a review by yourself.
• Added proper tests to cover this PR. (If tests are not applicable, explain.)
• Checked if this PR is a breaking (APIs have been changed) change.
• Checked if this PR will not introduce cross-platform inconsistent behavior.
• Checked if this PR would require a ReadMe/Wiki update.

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