multi: add blinded paths to invoices

Expose the ability to add blinded paths to an invoice. Also expose
various configuration values.

We also let the lncfg.Invoices struct satisfy the Validator interface so
that we can verify all its config values in one place.

log.go

@@ -22,6 +22,7 @@ import (
 	"github.com/lightningnetwork/lnd/healthcheck"
 	"github.com/lightningnetwork/lnd/htlcswitch"
 	"github.com/lightningnetwork/lnd/invoices"
+	"github.com/lightningnetwork/lnd/lncfg"
 	"github.com/lightningnetwork/lnd/lnrpc/autopilotrpc"
 	"github.com/lightningnetwork/lnd/lnrpc/chainrpc"
 	"github.com/lightningnetwork/lnd/lnrpc/devrpc"
@@ -181,6 +182,7 @@ func SetupLoggers(root *build.RotatingLogWriter, interceptor signal.Interceptor)
 	AddSubLogger(root, rpcwallet.Subsystem, interceptor, rpcwallet.UseLogger)
 	AddSubLogger(root, peersrpc.Subsystem, interceptor, peersrpc.UseLogger)
 	AddSubLogger(root, graph.Subsystem, interceptor, graph.UseLogger)
+	AddSubLogger(root, lncfg.Subsystem, interceptor, lncfg.UseLogger)
 }
 
 // AddSubLogger is a helper method to conveniently create and register the