Backup to public key

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Is your feature request related to a problem? Please describe

When using the API to create a backup, the decryption key must be known, because is uses symmetric encryption.

Describe the solution you'd like

I'd like to use a ssh key, as I would with Age. This way, I can script taking a backup without worrying about leaking the key to the backup. (API token is still a problem, but that would be remedied by having a token only capable of that specific operation.)

Describe alternatives you've considered

Submitting {"password": null} and then encrypting the backup using Age. Sort of works, I guess, but is unnecessarily involved.

Additional context

No response