Pass through parameters like `response_disposition` to `GoogleCloudStorage.url`

[nvn-nil]

Feature request

Use Case

Enable direct download of files stored using the GoogleCloudStorage class instead of viewing inline. This can be extended to a broader issue of having more control over the URL generation mechanism.

Current state

When we click on a URL generated for a file stored using GoogleCloudStorage, we navigate to the file instead of immediately triggering a download. This is the right behavior when we're using the file in code instead of downloading from a browser.

Proposed Solution

When generating the signed URL, we can pass the response_disposition argument or all kwargs through to generate_signed_url.

Passing the response_disposition 'attachment' (you can also add the filename here, but I don't use that) makes it a direct download link.
blob.generate_signed_url(expiration=self.settings.expiration, response_disposition="attachment", version="v4")

class GoogleCloudStorage(CompressStorageMixin, Storage):
    def url(self, name, **kwargs):
        """
        Return public url or a signed url for the Blob.
        This DOES NOT check for existance of Blob - that makes codes too slow
        for many use cases.
        """
        name = self._normalize_name(clean_name(name))
        blob = self.bucket.blob(name)
        blob_params = self.get_object_parameters(name)
        no_signed_url = (
            blob_params.get("acl", self.settings.default_acl) == "publicRead" or not self.settings.querystring_auth
        )

        if not self.settings.custom_endpoint and no_signed_url:
            return blob.public_url
        elif no_signed_url:
            return "{storage_base_url}/{quoted_name}".format(
                storage_base_url=self.settings.custom_endpoint,
                quoted_name=_quote(name, safe=b"/~"),
            )
        elif not self.settings.custom_endpoint:
            # Pass kwarg into the method
            return blob.generate_signed_url(expiration=self.settings.expiration, version="v4", **kwargs)
        else:
            # Pass kwarg into the method
            return blob.generate_signed_url(
                bucket_bound_hostname=self.settings.custom_endpoint,
                expiration=self.settings.expiration,
                version="v4",
                **kwargs
            )

This could also be a setting