Add response headers to presigned URL v4

[mortenpi]

This adds support for response-* query parameters for overriding response headers in v4 presigned URLs.

Right now, you can pass content_type to s3_sign_url, but it only does something for v2, and in v4 it is ignored. So here I am adding Content-Type + all the other supported ones, but only to v4 (as the v2 version seems to be deprecated).

It was a bit of a trial and error to figure out how exactly they should be incorporated into the signing process, but it seems to work:

AWSS3.s3_sign_url(
    aws_config, bucket, key, 60;
    verb="GET",
    signature_version="v4",
    protocol="https",
    content_type = "text/html",
    content_disposition = "attachment",
    content_language = "de-DE, en-CA",
    expires = Dates.format(now() + Dates.Hour(1), Dates.RFC1123Format),
    cache_control = "private, no-cache, no-store",
    content_encoding = "deflate",
)

leads to the following response when GETed:

HTTP/1.1 200 OK
x-amz-id-2: ...
x-amz-request-id: ...
Date: Fri, 27 Jan 2023 05:07:26 GMT
Last-Modified: Thu, 26 Jan 2023 00:09:10 GMT
ETag: "0797e3fead7383ee6f61c523c4582256"
x-amz-version-id: ...
Cache-Control: private, no-cache, no-store
Content-Disposition: attachment
Content-Encoding: deflate
Expires: Fri, 27 Jan 2023 19:07:24
Content-Language: de-DE, en-CA
Accept-Ranges: bytes
Content-Type: text/html
Server: AmazonS3
Content-Length: 93

If this broadly looks reasonable, them I'm happy to add some docs and tests as well.

[mortenpi]

Just a friendly bump -- it would still be nice to get this in.