Fix flyway-database-postgresql's transactional lock setting (#648)

The metadata for flyway-database-postgresql did not allow
org.flywaydb.database.postgresql.TransactionalModel to be serialized
to JSON. This resulted in a failure if the setTransactionalLock
method on PostgreSQLConfigurationExtension was called in a native
image.

This commit adds the necessary metadata and updates the existing
test to cover this code path.

Author: wilkinsona

metadata/org.flywaydb/flyway-database-postgresql/10.10.0/reflect-config.json

@@ -6,5 +6,13 @@
     },
     "allPublicConstructors": true,
     "allPublicMethods": true
+  },
+  {
+    "name": "org.flywaydb.database.postgresql.TransactionalModel",
+    "condition": {
+      "typeReachable": "org.flywaydb.core.internal.plugin.PluginRegister"
+    },
+    "allPublicConstructors": true,
+    "allPublicMethods": true
   }
 ]

tests/src/org.flywaydb/flyway-database-postgresql/10.10.0/src/test/java/flyway/database/postgresql/FlywayDatabasePostgresqlTests.java

@@ -17,6 +17,7 @@
 import org.flywaydb.core.api.configuration.Configuration;
 import org.flywaydb.core.api.configuration.FluentConfiguration;
 import org.flywaydb.core.api.output.MigrateResult;
+import org.flywaydb.database.postgresql.PostgreSQLConfigurationExtension;
 import org.junit.jupiter.api.AfterAll;
 import org.junit.jupiter.api.BeforeAll;
 import org.junit.jupiter.api.Test;
@@ -68,6 +69,9 @@ void migrate() {
                 .dataSource(dataSource)
                 .encoding(StandardCharsets.UTF_8)
                 .resourceProvider(new FixedResourceProvider());
+        configuration.getPluginRegister()
+                .getPlugin(PostgreSQLConfigurationExtension.class)
+                .setTransactionalLock(false);
 
         Flyway flyway = new Flyway(configuration);
         MigrateResult migration = flyway.migrate();