Non-blocking APIs for Durable Task clients

Issue summary

The DurableTaskClient APIs are all blocking APIs and use gRPC blocking-stubs internally. This limits the scalability of apps that depend on these client APIs.

Proposal

The DurableTaskClient abstract class should add support for non-blocking variants of the various APIs (starting orchestrations, waiting for their completion, etc.).

Other considerations

Azure Functions for Java doesn't yet support non-blocking functions: https://github.com/Azure/azure-functions-java-worker/issues/244, so non-blocking client APIs likely won't benefit Azure Functions users. Unfortunately, there's no indication about if or when this support will be added to Azure Functions.

從抽象類別 DurableTaskClient 開始，追蹤其 API 如何使用 gRPC blocking stub。定義用於啟動編排和等待完成的 non-blocking 變體，然後確認用戶端 API 不再需要 blocking 呼叫。