[improve][broker] Set log level to warn when topic policy reader occurs AlreadyClosedException

[Technoboy-]

Motivation

The AlreadyClosedException is a normal exception; the ERROR level log may trigger the monitor and confuse the user.
So suggest changing to WARN:

Sep 17 12:08:49 168-11-26-111 pulsar[23776]: 2022-09-17T12:08:49,510+0800 [broker-client-shared-internal-executor-6-1] ERROR org.apache.pulsar.broker.service.SystemTopicBasedTopicPoliciesService - Read more topic policies exception, close the read now!
Sep 17 12:08:49 168-11-26-111 pulsar[23776]: java.util.concurrent.CompletionException: org.apache.pulsar.client.api.PulsarClientException$AlreadyClosedException: The consumer which subscribes the topic MultiTopicsConsumer-6d140 with subscription name multiTopicsReader-9de778b249 was already closed when cleaning and closing the consumers
Sep 17 12:08:49 168-11-26-111 pulsar[23776]: at java.util.concurrent.CompletableFuture.encodeThrowable(CompletableFuture.java:331) ~[?:?]
Sep 17 12:08:49 168-11-26-111 pulsar[23776]: at java.util.concurrent.CompletableFuture.completeThrowable(CompletableFuture.java:346) ~[?:?]
Sep 17 12:08:49 168-11-26-111 pulsar[23776]: at java.util.concurrent.CompletableFuture$UniApply.tryFire(CompletableFuture.java:632) ~[?:?]
Sep 17 12:08:49 168-11-26-111 pulsar[23776]: at java.util.concurrent.CompletableFuture.postComplete(CompletableFuture.java:506) ~[?:?]
Sep 17 12:08:49 168-11-26-111 pulsar[23776]: at java.util.concurrent.CompletableFuture.completeExceptionally(CompletableFuture.java:2088) ~[?:?]
Sep 17 12:08:49 168-11-26-111 pulsar[23776]: at org.apache.pulsar.client.impl.ConsumerBase.failPendingReceives(ConsumerBase.java:274) 
Sep 17 12:08:49 168-11-26-111 pulsar[23776]: at org.apache.pulsar.client.impl.ConsumerBase.lambda$failPendingReceive$1(ConsumerBase.java:257) 
Sep 17 12:08:49 168-11-26-111 pulsar[23776]: at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128) ~[?:?]
Sep 17 12:08:49 168-11-26-111 pulsar[23776]: at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628) ~[?:?]
Sep 17 12:08:49 168-11-26-111 pulsar[23776]: at io.netty.util.concurrent.FastThreadLocalRunnable.run(FastThreadLocalRunnable.java:30)
Sep 17 12:08:49 168-11-26-111 pulsar[23776]: at java.lang.Thread.run(Thread.java:829) ~[?:?]
Sep 17 12:08:49 168-11-26-111 pulsar[23776]: Caused by: org.apache.pulsar.client.api.PulsarClientException$AlreadyClosedException: The consumer which subscribes the topic MultiTopicsConsumer-6d140 with subscription name multiTopicsReader-9de778b249 was already closed when cleaning and closing the consumers
Sep 17 12:08:49 168-11-26-111 pulsar[23776]: at org.apache.pulsar.client.impl.ConsumerBase.failPendingReceives(ConsumerBase.java:276) 
Sep 17 12:08:49 168-11-26-111 pulsar[23776]: ... 5 more

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Matching PR in forked repository

PR in forked repository: (https://github.com/Technoboy-/pulsar/pull/7)