Add response-content-disposition to url in Workhorse.send_url

Context

Previously, we fixed Generic Package Registry: downloading files fro... (#465102 - closed). However, Users reported that the bug still presents when downloading generic packages from the project release page.

After investigation, it turned out that we don't pass the response-content-disposition query param in the file URL that sent to Gitlab::Workhorse.send_url.

What does this MR do?

• Add the response-content-disposition query param to the file URL that passed to Gitlab::Workhorse.send_url. Same as we do here.
• Add related specs.

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Before	After

How to set up and validate locally

1. Add proxy_download: true setting to your GDK's config > gitlab.yml > {} production > {} packages > {} object_store and restart the GDK.
2. Follow those steps to publish a release with a generic package and download it with the correct name.

Related to #492354 (closed)