[FLINK-35524][cdc-base] Clear connections pools when reader exist.

[loserwang1024]

Current, inJdbcConnectionPools is static instance, so the datasource pools in it won't be recycle when reader close. It will cause memory leak.

public class JdbcConnectionPools implements ConnectionPools<HikariDataSource, JdbcSourceConfig> {

private static final Logger LOG = LoggerFactory.getLogger(JdbcConnectionPools.class);

private static JdbcConnectionPools instance;
private final Map<ConnectionPoolId, HikariDataSource> pools = new HashMap<>();
private static final Map<String, JdbcConnectionPoolFactory> POOL_FACTORY_MAP = new HashMap<>();

[loserwang1024]

@Jiabao-Sun @GOODBOY008 @PatrickRen @leonardBang , CC

[leonardBang]

Thanks @loserwang1024 for the contribution, could you rebase to latest master?
@ruanhang1993 Would you like to take a look again?

[ruanhang1993]

LGTM.