Min swap fee

When doing a trade, our slip based fee model allows the fee to go to zero for very small trades. We should create a mimir controlled floor. One for trades that include a synth, and one that is for L1 (non-native assets).

Logic should be

if sourceAsset or targetAsset is L1
 apply L1 floor
elif sourceAsset or targetAsset is synth
 apply synth floor
}