[Feature Request] Ability to set download url.

[ChromoX]

Hello,

I am a user of kopia with Backblaze. Thanks for your work on this project.

There is a partnership that Backblaze and Cloudflare have. This allows for the potential of downloading items from your buckets without paying the download fee. In the past I've used rclone and they had a simple command line option https://rclone.org/b2/#b2-download-url that would allow you to point the download url to the Cloudflare URL.

I don't have any experience in Go, but if you need any other information or would like help testing please let me know.

More information:
https://help.backblaze.com/hc/en-us/articles/217666928-Using-Backblaze-B2-with-the-Cloudflare-CDN