[Feature] Support attributes in sign/sign_async

The `sign` method and it's async counterpart `sign_async` don't support `attributes` such as (response)-content-disposition, filename, etc... which can be useful when then signed url is meant for a browser download.

Is it feasible to add such a feature? I assume the list of supported attributes would boil down to
- (S3/Azure/GCS) content-disposition
- (S3/Azure/GCS) content-type
- (S3/Azure) content-encoding
- (S3/Azure) cache-control
- (S3/Azure) content-language

Which are all supported S3/Azure, but GCS doesn't seem to support the last 3.

Start by locating the sign and sign_async entry points and how they handle S3, Azure, and GCS options. Compare provider support for the listed response attributes, then add coverage showing that supported attributes appear in generated signed URLs while unsupported combinations remain well-defined.

Written by the indexing model from the issue text.