Cross-language, cross-library tests timing out for China cloud

Because our test pipeline agents run from somewhere in the US and do, perhaps, to some other issues, many of our tests across libraries and languages are timing out against the China cloud e.g., Azure/azure-sdk-for-net#34641 (manual test run, but indicative of tests-weekly runs).

Discussing this offline, we could expose some variable in cloud-specific files e.g., https://github.com/Azure/azure-sdk-tools/blob/main/eng/common/TestResources/clouds/AzureChinaCloud.json, that get plumbed through to clients.

Review eng/common/TestResources/clouds/AzureChinaCloud.json and the Azure/azure-sdk-for-net#34641 timeout example first. Trace how cloud-specific settings reach test clients across the pipeline. Done means a documented cloud-specific value can be exposed and consumed where needed to address China cloud test timeouts.

Written by the indexing model from the issue text.