Flaky test: ProducerTest.testWaitForExclusiveProducer

[example failure](https://github.com/apache/pulsar-client-cpp/actions/runs/3589998748/jobs/6042967481)

```
FAILED TESTS (1/376):
166 ms: ./pulsar-tests ProducerTest.testWaitForExclusiveProducer (try #1)
```

```
[ RUN ] ProducerTest.testWaitForExclusiveProducer
2022-12-01 06:25:37.989 INFO [140250769911488] ClientConnection:189 | [ -> pulsar://localhost:6650] Create ClientConnection, timeout=10000
2022-12-01 06:25:37.989 INFO [140250769911488] ConnectionPool:97 | Created connection for pulsar://localhost:6650
2022-12-01 06:25:37.991 INFO [140250766808640] ClientConnection:379 | [[::1]:37744 -> [::1]:6650] Connected to broker
2022-12-01 06:25:37.997 INFO [140250766808640] HandlerBase:72 | [persistent://public/default/testWaitForExclusiveProducer1669875937, p-name-1] Getting connection from pool
2022-12-01 06:25:38.038 INFO [140250766808640] ProducerImpl:190 | [persistent://public/default/testWaitForExclusiveProducer1669875937, p-name-1] Created producer on broker [[::1]:37744 -> [::1]:6650]
2022-12-01 06:25:38.043 INFO [140250769911488] ProducerImpl:721 | [persistent://public/default/testWaitForExclusiveProducer1669875937, p-name-1] Closing producer for topic persistent://public/default/testWaitForExclusiveProducer1669875937
2022-12-01 06:25:38.044 INFO [140250766808640] ProducerImpl:687 | [persistent://public/default/testWaitForExclusiveProducer1669875937, p-name-1] Closed producer 0
2022-12-01 06:25:38.045 INFO [140250766808640] HandlerBase:72 | [persistent://public/default/testWaitForExclusiveProducer1669875937, p-name-2] Getting connection from pool
2022-12-01 06:25:38.053 INFO [140250766808640] ProducerImpl:190 | [persistent://public/default/testWaitForExclusiveProducer1669875937, p-name-2] Created producer on broker [[::1]:37744 -> [::1]:6650]
/home/runner/work/pulsar-client-cpp/pulsar-client-cpp/tests/ProducerTest.cc:331: Failure
Expected equality of these values:
ResultOk
Which is: Ok
producer2.send(MessageBuilder().setContent("content").build())
Which is: ProducerNotInitialized
```

tests/ProducerTest.cc の 331 行目から始め、リンクされた CI の失敗をベースラインとして ProducerTest.testWaitForExclusiveProducer を実行します。producer2 の初期化と send シーケンスを追跡し、なぜ send が ProducerNotInitialized を観測する可能性があるのかを特定します。テストが確実に成功し、exclusive-producer の動作が維持されれば完了です。

索引モデルが issue の本文から書いたものです。