AWS V4 Signer canonical headers list doesn't matches specification

[HKTRp]

Describe the bug
According to the AWS specification, canonical headers list must include Content-Type header. In current AWS4Signer implementation there is Content-MD5 header instead.

To Reproduce
Just use aws v4 signer.

Which AWS service(s) are affected?
It may affect S3, especially not an AWS ones implementations.

Expected behavior
Include Content-Type in Canonical headers list.

[thisisabhash]

Thank you for posting this - our team will take a look.