lnd: make the payment schema migration available for testing

We allow the migration of the payment schema to be applied when
the test_native_sql is active to make sure the tables are properly
contructed.

sqldb/migrations_dev.go

@@ -2,4 +2,10 @@
 
 package sqldb
 
-var migrationAdditions []MigrationConfig
+var migrationAdditions = []MigrationConfig{
+	{
+		Name:          "000009_payments",
+		Version:       11,
+		SchemaVersion: 9,
+	},
+}