Upgrade scratchstack-aws-signature to its latest version

[HatemMn]

Goal

Upgrading this crate will empty the deny.toml from ignored advisories

Dev Guide

This library has taken a breaking change and there is this **migration guide ** : https://docs.rs/scratchstack-aws-signature/latest/scratchstack_aws_signature/migration/index.html

It does lack more details...

In a previous PR that we didn't merge, I did the work by creating a dummy error type in order to avoid using the box dependency, and I managed to pass the upgrade by creating this closure :

 // service_for_signing_key_fn wraps an async fn into the tower::Service
            // required by sigv4_validate_request, so we don't have to implement
            // the Service trait manually - hence the creation of the closure below.
            let get_signing_key = move |req: GetSigningKeyRequest| {

The full can be found here : https://github.com/Cosmian/kms/blob/63141e1cc7f55cee810efd2b9ce5dbefada5fe54/crate/server/src/routes/aws_xks/sigv4_middleware.rs

You can copy paste it if it still compiles the day we will make the upgrade

For more info, check the previous PR : https://github.com/Cosmian/kms/pull/866/changes#diff-2e9d962a08321605940b5a657135052fbcef87b5e360662bb527c96d9a615542