Add support for S3 presigned requests (#731)

* Refactor inlineables so that they can be made public

* Clean up HttpProtocolGenerator

* Add presigning inline module

* Add synthetic presignable trait to known operations

* Stub out input `presigned` method

* Add example of presigning GetObject with the input

* Generate `presigned` on fluent builders

* Wire up `presign` to the AWS middleware

* Add example for S3 PutObject presigned

* Wire up middleware to query param signer

* Fix query param signing with security tokens

* Clean up AwsPresigningDecorator and add RustSettings to decorators

* Add test for presigned S3 GetObject and fix issues discovered

* Add doc comments to aws-inlineable

* Update changelog

* Revert addition of RustSettings to decorators

* Incorporate feedback

* Fix CI

* Improve doc comment