Support SigV4a multi-region

[rjmackay]

Is it feasible to extend this to support multi-region signatures?

[markwainwright]

Big +1 on this. It doesn't seem to be possible to make requests to S3 Multi-Region Access Points from a Cloudflare Worker, because the AWS SDK uses a native binary to generate SigV4As and that isn't supported on that platform. It would be amazing to have a native JavaScript alternative, if such a thing is feasible.