itest: graph sql migration itest

This commit adds a basic itest that is run under the `test_native_sql`
flag. It tests that the migration is idempotent and that the node cant
be restarted without the `db.use-native-sql` flag once the graph
migration has been run.

itest/list_on_test.go

@@ -683,6 +683,10 @@ var allTestCases = []*lntest.TestCase{
 		Name:     "invoice migration",
 		TestFunc: testInvoiceMigration,
 	},
+	{
+		Name:     "graph migration",
+		TestFunc: testGraphMigration,
+	},
 	{
 		Name:     "payment address mismatch",
 		TestFunc: testWrongPaymentAddr,