Fix presigning bug with `content-length` and `content-type` in S3 (#1216)

* Fix presigning bug with `content-length` and `content-type` in S3

* Fix presigning test in `aws-sigv4`

* Update changelog

* Clean when generating code for diff preview

* Incorporate feedback

* Fix server codegen

Co-authored-by: Zelda Hessler <zhessler@amazon.com>