Use ledger to validate externally signed transactions in CdW

[paolino]

Why

ATM externally signed transactions are passed through, which is a feature, but we do not have feedback about their validity if not from the node.

What

Add a ledger based pre-check on externally signed txs during the state change,

cardano-wallet/lib/ui/src/Cardano/Wallet/UI/Deposit/API/Payments.hs

Lines 308 to 309 in 0e7b650

	step _ (Unsigned utx) (ExternallySign stx) = do
	pure $ Just $ Signed utx stx

Notes

It will involve a more sophisticated behavior so that we can track the state transition failure reason.