Improve error messaging: Invalid argument: address f8d6e0586b0a20c7 is invalid for chain flow-mainnet

[justjoolz]

Issue To Be Solved

Invalid argument: address f8d6e0586b0a20c7 is invalid for chain flow-mainnet

Improve error messaging in this case the error occurs because the cli defaults to signing a tx with the emulator-account

This isn't obvious from the error message

(Optional): Suggest A Solution

Add message to say when attempting to use a default signer as none is provided. If the tx specified to be sent requires a signer and none is provided, warn the user.