Ensure that direct upload works

[plabaj]

Ensuring that direct uploads work with Bunny

• Updated the url_for_direct_upload method to generate a URL based on the region and storage_zone attributes.
• Modified the headers_for_direct_upload method to include the access_key and set the Content-Type to 'application/octet-stream'.
• Added a custom_metadata_headers method that currently returns an empty hash.

[rkwap]

@plabaj Thanks for raising the PR. Will check over this weekend.