Using Flink 1.20.3, starting sql-client.sh throws 'Failed to start th…

[Cocoyamsweetsnow]

…e embedded sql-gateway' error

What problem does this PR solve?

Issue Number: close #60983

Related PR: None

Problem Summary:
在 Flink 1.20+ 中，sql-client.sh 的行为发生了重大变更：不再直接连接 JobManager
的 REST 端点，而是在本地启动一个嵌入式 SQL Gateway。该嵌入式网关在未显式配置
sql-gateway.endpoint.rest.port 时，会继承全局的 rest.bind-port（默认 8081）
作为自己的 REST 端口。
由于 JobManager 的 REST 端点已经占用了 8081，嵌入式 SQL Gateway 尝试绑定同一端口时
就会抛出以下异常：
java.net.BindException: Could not start rest endpoint on any port in port range 8081 at org.apache.flink.runtime.rest.RestServerEndpoint.start at org.apache.flink.table.gateway.SqlGateway.start

修复方案：
在 samples/datalake/iceberg_and_paimon/data/flink-conf/flink-conf.yaml 中新增
sql-gateway.endpoint.rest.port: 9091，为嵌入式 SQL Gateway 指定一个独立端口，
使其与 JobManager REST 端口（8081）隔离，避免端口冲突。

Release note

When using Flink 1.20+ with sql-client.sh, add sql-gateway.endpoint.rest.port
configuration to avoid port conflict with JobManager's REST endpoint.

Check List (For Author)

• Test
  • No need to test or manual test. Explain why:
    • This is a refactor/code format and no logic has been changed.
    • No runtime logic changed; only a configuration sample file is updated.
• Behavior changed:
  • No.
• Does this need documentation?
  • No.

Check List (For Reviewer who merge this PR)

• Confirm the release note
• Confirm test cases
• Confirm document
• Add branch pick label

[hello-stephen]

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[morningman]

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