Fix: Automated Escrow deposit for sender not signer

[hopeyen]

Problem statement

Realising that the downloader must run as a signer and not sender, the previous --max-auto-deposit submits GRT approval and Escrow deposit ran during download would be done on behave of the signer, which is incorrect.

Expectation proposal

While it is fairly easy to run the CLI command manually with the sender wallet, it would be good to let downloader take in an secondary mnemonic/private such that manual work is not needed.
Update auto payment to use the sender wallet.