Preconf RPC improvements: Withdraw balance from gas tank

[aloknerurkar]

Currently the user can only deposit balance into the gas tank and check his/her balance using the mevcommit_getBalance RPC. We should also have the option to withdraw the balance if the user wishes to do so. This will issue a transaction through the preconf RPC itself to send ETH back to the sender account. The user should be charged for the bid and remaining amount will be transferred back to his EOA account.