brokerClientAuthenticationPlugin param doesn't restore to default after deletion dynamic config value

**To Reproduce**

You can start Pulsar in docker with:

`docker run -it -p 8080:8080 apachepulsar/pulsar:2.10.0 bin/pulsar standalone`

Check the default value:

Set new value:

Delete dynamic config and check runtime config.

My expectation is that the value should be `org.apache.pulsar.client.impl.auth.AuthenticationDisabled` again.

But it's not:

Broker's logs tell us that the value has been deleted.

```
### Broker logs

pulsar_1 | 2022-06-18T09:42:26,274+0000 [main-EventThread] INFO org.apache.pulsar.broker.admin.impl.BrokersBase - [null] Successfully to delete dynamic configuration brokerClientAuthenticationPlugin
pulsar_1 | 2022-06-18T09:42:26,277+0000 [main-EventThread] INFO org.eclipse.jetty.server.RequestLog - 172.18.0.1 - - [18/Jun/2022:09:42:26 +0000] "DELETE /admin/v2/brokers/configuration/brokerClientAuthenticationPlugin HTTP/1.1" 200 0 "-" "Pulsar-Java-v2.10.0" 12
```

Reproduce the issue with the provided Pulsar 2.10.0 Docker command, then set and delete brokerClientAuthenticationPlugin through the shown broker configuration endpoint. Trace the broker's dynamic-configuration handling and compare the runtime value with the default; done means deleting the dynamic value restores org.apache.pulsar.client.impl.auth.AuthenticationDisabled.

Written by the indexing model from the issue text.