[postgres] Add commits of PostgresConnection back to distinguish with debezium's origin class (#2839)

Author: loserwang1024

flink-cdc-connect/flink-cdc-source-connectors/flink-connector-postgres-cdc/src/main/java/io/debezium/connector/postgresql/connection/PostgresConnection.java

@@ -54,6 +54,14 @@
  * {@link JdbcConnection} connection extension used for connecting to Postgres instances.
  *
  * @author Horia Chiorean
+ *     <p>Copied from Debezium 1.9.2-Final with two additional methods:
+ *     <ul>
+ *       <li>Constructor PostgresConnection( Configuration config, PostgresValueConverterBuilder
+ *           valueConverterBuilder, ConnectionFactory factory) to allow passing a custom
+ *           ConnectionFactory
+ *       <li>override connection() to return a unwrapped PgConnection (otherwise, it will complain
+ *           about HikariProxyConnection cannot be cast to class org.postgresql.core.BaseConnection)
+ *     </ul>
  */
 public class PostgresConnection extends JdbcConnection {