tidb-cloud: the broker hostname form is inconsistent in the Alibaba Cloud Kafka private link guide #24495

In tidb-cloud/serverless-private-link-connection-to-self-hosted-kafka-in-alicloud.md, the broker hostname in the EXTERNAL advertised listeners uses two different forms:

• Without the zone: <broker_id>.unique_name.alicloud.plc.tidbcloud.com:<port>
  • the Kafka Advertised Listener Pattern in the prerequisites table (line 56) and the configuration comments (lines 225, 244, 263, 473, 488, 503)
  • broker 1 and broker 2 in server.properties (lines 232, 251)
  • all three brokers in the reconfiguration steps (lines 475, 490, 505)
  • the expected output at lines 339-341 and 636-638
• With the zone: <broker_id>.<zone>.unique_name.alicloud.plc.tidbcloud.com:<port>
  • broker 3 in server.properties (line 270: b3.ap-southeast-1c.unique_name.alicloud.plc.tidbcloud.com:9095)
  • the expected output at lines 536-538 (b1.ap-southeast-1a…, b2.ap-southeast-1b…, b3.ap-southeast-1c…)
  • line 204 also says that "AZ ID in Kafka Advertised Listener Pattern indicates where the broker is deployed", but the pattern at line 56 has no zone.

Users who copy these examples can configure different hostnames for the same broker. Which form TiDB Cloud expects for Alibaba Cloud needs to be confirmed, and then the guide should use that form everywhere. (The AWS version of this guide includes the AZ ID in the pattern, so the zone form might have been copied from it.)

Found while reviewing #24487, which fixes a different typo in this file (the broker ID in a comment).