cmd/lncli: update ad-hoc addinvoice response json to display add_index

cmd/lncli/commands.go

@@ -2194,9 +2194,11 @@ func addInvoice(ctx *cli.Context) error {
 	printJSON(struct {
 		RHash    string `json:"r_hash"`
 		PayReq   string `json:"pay_req"`
+		AddIndex uint64 `json:"add_index"`
 	}{
 		RHash:    hex.EncodeToString(resp.RHash),
 		PayReq:   resp.PaymentRequest,
+		AddIndex: resp.AddIndex,
 	})
 
 	return nil