WIP Midnight bridge: withdrawals

[ladislavdubravsky]

Testing

../../target/debug/sov-cli keys import --path demo_data/midnight_bridge_signer.json --nickname demo

# send withdraw transaction
../../target/debug/sov-cli transactions import from-file midnight-withdrawals --path withdraw_night.json --max-fee 1000000000
../../target/debug/sov-cli node submit-batch by-nickname demo

# balance checking
curl http://127.0.0.1:12346/modules/bank/tokens/gas_token/balances/sov1lzkjgdaz08su3yevqu6ceywufl35se9f33kztu5cu2spja5hyyf
# withdrawal "proof"
curl http://127.0.0.1:12346/modules/midnight-withdrawals/withdrawals/0