[fix] [broker] Fix metrics pulsar_topic_load_failed_count is 0 when load non-persistent topic fails and fix the flaky test testBrokerStatsTopicLoadFailed

[poorbarcode]

Fixes: #20495

Motivation

1. The test BrokerServiceTest.testBrokerStatsTopicLoadFailed always fails, so [fix][test] Disable invalid test BrokerServiceTest#testBrokerStatsTopicLoadFailed #20494 disabled it.
2. There is a case that pulsar_topic_load_failed_count does not increase when load non-persistent topic fails^[1].

---

[1]: https://github.com/apache/pulsar/blob/master/pulsar-broker/src/main/java/org/apache/pulsar/broker/service/BrokerService.java#L1239-L1258

CompletableFuture<Optional<Topic>> topicFuture = new CompletableFuture<>();
topicFuture.exceptionally(t -> {
    pulsarStats.recordTopicLoadFailed();
    return null;
});
try {
    nonPersistentTopic = newTopic(topic, null, this, NonPersistentTopic.class);
} catch (Throwable e) {
    log.warn("Failed to create topic {}", topic, e);
    // Highlight: It is a new future, so the event `topicFuture.exceptionally` will not receive the error callback anymore.
    return FutureUtil.failedFuture(e);
}

Modifications

1. fix the test.
2. fix the issue

Documentation

• doc
• doc-required
• doc-not-needed
• doc-complete

Matching PR in forked repository

PR in forked repository: x

[poorbarcode]

/pulsarbot rerun-failure-checks

[poorbarcode]

Rebase master