feature: define new feature bit for bolt11 blinded paths

We need a new feature bit for BOLT11 invoices in order to indicate that
they contain the new blinded path tagged field. Tagged fields pre-date
TLV and so nodes who dont understand them will simply skip them.
Therefore the feature bit helps them to fail fast.

feature/default_sets.go

@@ -92,4 +92,7 @@ var defaultSetDesc = setDesc{
 		SetInit:    {}, // I
 		SetNodeAnn: {}, // N
 	},
+	lnwire.Bolt11BlindedPathsOptional: {
+		SetInvoice: {}, // I
+	},
 }