feat(transfer): consider supporting transferring to own accounts with flag `--to-account <ix>`

This was a feature that I thought of possibly supporting in FuelLabs/forc-wallet#103 but did not end up implementing in that PR, but it would be convenient to be able to transfer to your own wallet using your account index rather than having to know your address.

This isn't a critical feature since we can transfer using addresses, but is a nice to have!