lnwallet: add new aux resolver interface

This will be used by external callers to modify the way we resolve
contracts on chain. For a given contract, we'll store an extra "blob",
that will later be presented during the sweeping phase.

config_builder.go

@@ -187,6 +187,10 @@ type AuxComponents struct {
 	// AuxChanCloser is an optional channel closer that can be used to
 	// modify the way a coop-close transaction is constructed.
 	AuxChanCloser fn.Option[chancloser.AuxChanCloser]
+
+	// AuxContractResolver is an optional interface that can be used to
+	// modify the way contracts are resolved.
+	AuxContractResolver fn.Option[lnwallet.AuxContractResolver]
 }
 
 // DefaultWalletImpl is the default implementation of our normal, btcwallet