fix(sigv4): Default to non-chunked payloads for S3

This was made the default since it's much more efficient, especially on web for large uploads, but some S3 operations do not support it so it should not be the default. Instead, it will be selectively enabled in the SDK layer for operations which allow it.

commit-id:0c690d3f

Author: Dillon Nys

packages/aws_signature_v4/lib/src/configuration/services/s3.dart

@@ -74,7 +74,7 @@ class S3ServiceConfiguration extends BaseServiceConfiguration {
   /// {@macro aws_signature_v4.s3_service_configuration}
   S3ServiceConfiguration({
     this.signPayload = true,
-    this.chunked = true,
+    this.chunked = false,
     int chunkSize = _defaultChunkSize,
     this.encoding = S3PayloadEncoding.none,
   })  : assert(