Secured sandbox auto signature (#845)

Some users report that JS/Python types lack a `useSignature` attribute,
which only works when `secure=true` is set for the sandbox. This change
removes the `useSignatrue` parameter and makes all upload/download URL
requests signed if `secure` was provided, making sure the function will
work for all possible cases.

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Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>
Co-authored-by: Ben Fornefeld <50748440+ben-fornefeld@users.noreply.github.com>