Flaky test: KeyBasedBatchingTest.testOrderingKeyPriority

[example failure](https://github.com/apache/pulsar-client-cpp/actions/runs/3911569384/jobs/6685111475)

```
FAILED TESTS (5/399):
255 ms: ./pulsar-tests ClientTest.testReferenceCount (try #1)
177 ms: ./pulsar-tests ClientTest.testReferenceCount (try #2)
679 ms: ./pulsar-tests ClientTest.testReferenceCount (try #3)
260 ms: ./pulsar-tests ClientTest.testReferenceCount (try #4)
9421 ms: ./pulsar-tests KeySharedConsumerTest.testOrderingKeyPriority (try #1)
```

Run log:
```
[ RUN ] KeySharedConsumerTest.testOrderingKeyPriority
2023-01-13 13:18:03.900 INFO [139656847097536] ClientConnection:190 | [ -> pulsar://localhost:6650] Create ClientConnection, timeout=10000
2023-01-13 13:18:03.900 INFO [139656847097536] ConnectionPool:97 | Created connection for pulsar://localhost:6650
2023-01-13 13:18:03.904 INFO [139656843974208] ClientConnection:387 | [[::1]:56998 -> [::1]:6650] Connected to broker
2023-01-13 13:18:03.907 INFO [139656843974208] HandlerBase:72 | [persistent://public/default/KeySharedConsumerTest-ordering-key-priority1673615883, ] Getting connection from pool
2023-01-13 13:18:03.943 INFO [139656843974208] ProducerImpl:202 | [persistent://public/default/KeySharedConsumerTest-ordering-key-priority1673615883, ] Created producer on broker [[::1]:56998 -> [::1]:6650]
2023-01-13 13:18:03.943 INFO [139656847097536] Client:87 | Subscribing on Topic :KeySharedConsumerTest-ordering-key-priority1673615883
2023-01-13 13:18:03.944 INFO [139656843974208] HandlerBase:72 | [persistent://public/default/KeySharedConsumerTest-ordering-key-priority1673615883, SubscriptionName, 0] Getting connection from pool
2023-01-13 13:18:03.958 INFO [139656843974208] ConsumerImpl:239 | [persistent://public/default/KeySharedConsumerTest-ordering-key-priority1673615883, SubscriptionName, 0] Created consumer on broker [[::1]:56998 -> [::1]:6650]
2023-01-13 13:18:03.958 INFO [139656847097536] Client:87 | Subscribing on Topic :KeySharedConsumerTest-ordering-key-priority1673615883
2023-01-13 13:18:03.959 INFO [139656843974208] HandlerBase:72 | [persistent://public/default/KeySharedConsumerTest-ordering-key-priority1673615883, SubscriptionName, 1] Getting connection from pool
2023-01-13 13:18:03.960 INFO [13965684397[420](https://github.com/apache/pulsar-client-cpp/actions/runs/3911569384/jobs/6685111475#step:9:421)8] ConsumerImpl:239 | [persistent://public/default/KeySharedConsumerTest-ordering-key-priority1673615883, SubscriptionName, 1] Created consumer on broker [[::1]:56998 -> [::1]:6650]
2023-01-13 13:18:03.961 INFO [139656847097536] Client:87 | Subscribing on Topic :KeySharedConsumerTest-ordering-key-priority1673615883
2023-01-13 13:18:03.961 INFO [139656843974208] HandlerBase:72 | [persistent://public/default/KeySharedConsumerTest-ordering-key-priority1673615883, SubscriptionName, 2] Getting connection from pool
2023-01-13 13:18:03.962 INFO [139656843974208] ConsumerImpl:239 | [persistent://public/default/KeySharedConsumerTest-ordering-key-priority1673615883, SubscriptionName, 2] Created consumer on broker [[::1]:56998 -> [::1]:6650]
2023-01-13 13:18:13.157 INFO [139656847097536] KeySharedConsumerTest:124 | messagesPerConsumer: {0 => 506, 1 => 217, 2 => 277}
/home/runner/work/pulsar-client-cpp/pulsar-client-cpp/tests/KeySharedConsumerTest.cc:135: Failure
Expected: (fabs(count - expectedMessagesPerConsumer)) < (expectedMessagesPerConsumer * PERCENT_ERROR), actual: 172.667 vs 166.667
2023-01-13 13:18:13.157 INFO [139656847097536] ClientImpl:535 | Closing Pulsar client with 1 producers and 3 consumers
2023-01-13 13:18:13.157 INFO [139656847097536] ProducerImpl:742 | [persistent://public/default/KeySharedConsumerTest-ordering-key-priority1673615883, standalone-0-377] Closing producer for topic persistent://public/default/KeySharedConsumerTest-ordering-key-priority1673615883
2023-01-13 13:18:13.158 INFO [139656847097536] ConsumerImpl:1119 | [persistent://public/default/KeySharedConsumerTest-ordering-key-priority1673615883, SubscriptionName, 2] Closing consumer for topic persistent://public/default/KeySharedConsumerTest-ordering-key-priority1673615883
2023-01-13 13:18:13.158 INFO [139656843974208] ProducerImpl:706 | [persistent://public/default/KeySharedConsumerTest-ordering-key-priority1673615883, standalone-0-377] Closed producer 0
2023-01-13 13:18:13.158 INFO [139656847097536] ConsumerImpl:1119 | [persistent://public/default/KeySharedConsumerTest-ordering-key-priority1673615883, SubscriptionName, 1] Closing consumer for topic persistent://public/default/KeySharedConsumerTest-ordering-key-priority1673615883
2023-01-13 13:18:13.158 INFO [139656843974208] ConsumerImpl:1105 | [persistent://public/default/KeySharedConsumerTest-ordering-key-priority1673615883, SubscriptionName, 2] Closed consumer 2
2023-01-13 13:18:13.159 INFO [139656847097536] ConsumerImpl:1119 | [persistent://public/default/KeySharedConsumerTest-ordering-key-priority1673615883, SubscriptionName, 0] Closing consumer for topic persistent://public/default/KeySharedConsumerTest-ordering-key-priority1673615883
2023-01-13 13:18:13.159 INFO [139656843974208] ConsumerImpl:1105 | [persistent://public/default/KeySharedConsumerTest-ordering-key-priority1673615883, SubscriptionName, 1] Closed consumer 1
2023-01-13 13:18:13.159 INFO [139656843974208] ConsumerImpl:1105 | [persistent://public/default/KeySharedConsumerTest-ordering-key-priority1673615883, SubscriptionName, 0] Closed consumer 0
2023-01-13 13:18:13.160 INFO [139656793630272] ClientConnection:1648 | [[::1]:56998 -> [::1]:6650] Connection disconnected
2023-01-13 13:18:13.160 INFO [139656793630272] ClientConnection:268 | [[::1]:56998 -> [::1]:6650] Destroyed connection
2023-01-13 13:18:13.161 INFO [139656847097536] ProducerImpl:699 | Producer - [persistent://public/default/KeySharedConsumerTest-ordering-key-priority1673615883, standalone-0-377] , [batching = off]
[ FAILED ] KeySharedConsumerTest.testOrderingKeyPriority (9262 ms)
[----------] 1 test from KeySharedConsumerTest (9262 ms total)

[----------] Global test environment tear-down
[==========] 1 test from 1 test suite ran. (9262 ms total)
[ PASSED ] 0 tests.
[ FAILED ] 1 test, listed below:
[ FAILED ] KeySharedConsumerTest.testOrderingKeyPriority
```

まず KeySharedConsumerTest.testOrderingKeyPriority を実行し、consumer ごとのメッセージ数が確認されている tests/KeySharedConsumerTest.cc の 135 行目付近を読みます。観測された分布を期待される許容範囲と比較し、ordering-key priority test が断続的に失敗する理由を調査します。ordering または distribution のチェックを弱めることなく、テストが確実に成功するようになれば完了です。

索引モデルが issue の本文から書いたものです。