[sdk-platform-java] Unable to test end to end configuration options

Code that glues ClientSettings to the ClientContext is generated by gapic generator making it difficult to test that configuration options make it to the transport layer.

Can we generate a test client where we can mock out the transport for testing purposes?

首先定位 sdk-platform-java 中将 ClientSettings 连接到 ClientContext 的 gapic 生成器代码，然后跟踪传输层的生成方式。定义生成的测试客户端的传输模拟接缝，并验证配置选项能够传递到模拟传输；当端到端测试无需真实传输即可测试这些选项时，即视为完成。

由索引模型根据 Issue 内容生成。