:query_params option for aws_sigv4_url/1

[balexand]

This adds support for adding query params to presigned URLs. S3 allows response headers to be overridden using query params such as response-cache-control, response-content-disposition, response-content-encoding, etc. See https://docs.aws.amazon.com/AmazonS3/latest/API/API_GetObject.html for details.

I've tested this implementation by making requests to S3 with response-content-disposition and response-cache-control.

If this gets merged then I'll submit a separate pull-request to add support for this to ReqS3.presign_url/1.

Thanks!

[balexand]

This is a duplicate of #445