Reload configuration more frequently in apply worker.

Reload configuration more frequently in apply worker.

The apply worker was not reloading the configuration while processing
messages if there is a continuous flow of messages from upstream. It was
also not reloading the configuration if there is a change in the
configuration after it has waited for the message and before receiving the
new replication message. This can lead to failure in tests because we
expect that after reload, the behavior of apply worker to respect the
changed GUCs.

We found this while analyzing a rare buildfarm failure.

Author: Hou Zhijie
Reviewed-by: Amit Kapila
Discussion: https://postgr.es/m/OS0PR01MB5716AF9079CC0755CD015322947E9@OS0PR01MB5716.jpnprd01.prod.outlook.com