rpcserver+invoicesrpc: alias-aware AddInvoice,AddHoldInvoice rpc

AddInvoice,AddHoldInvoice now issue invoices that include our
peer's aliases. Some extra sanity checks are included to ensure we
don't leak our confirmed SCID for a private channel.

lnrpc/invoicesrpc/config_active.go

@@ -60,4 +60,8 @@ type Config struct {
 	// GenAmpInvoiceFeatures returns a feature containing feature bits that
 	// should be advertised on freshly generated AMP invoices.
 	GenAmpInvoiceFeatures func() *lnwire.FeatureVector
+
+	// GetAlias returns the peer's alias SCID if it exists given the
+	// 32-byte ChannelID.
+	GetAlias func(lnwire.ChannelID) (lnwire.ShortChannelID, error)
 }