Normal Swaps: Fail Swap If Overpayment >2x

[kilrau]

In line with lightning specs, we should fail normal swaps that have chain overpayments of more than >2x as this is very likely a user error. User's mostly fatfinger "one 0 too much". This would add automation to overpayment refunds that we are currently handling manually (and rely on users contacting us).

PS: Elegant handling of overpayments via covenants (https://github.com/BoltzExchange/boltz-backend/issues/464) will only work on liquid. Overpayments on RSK should be avoidable.