multi: query circuit map inside contractcourt

This commit adds a new config method `QueryIncomingCircuit` that can be
used to query the payment's incoming circuit for giving its outgoing
circuit key.

contractcourt/htlc_incoming_contest_resolver_test.go

@@ -352,6 +352,11 @@ func newIncomingResolverTestContext(t *testing.T, isExit bool) *incomingResolver
 			},
 			HtlcNotifier: htlcNotifier,
 			Budget:       *DefaultBudgetConfig(),
+			QueryIncomingCircuit: func(
+				circuit models.CircuitKey) *models.CircuitKey {
+
+				return nil
+			},
 		},
 		PutResolverReport: func(_ kvdb.RwTx,
 			_ *channeldb.ResolverReport) error {