allow selection of workspace proxy


We deploy a set of workspace proxies around the world with a certain service provider.
That provider recently had an outage, and this appears to have lead to higher-than-normal latency on the proxy closest to me (Johannesburg). The proxy with the lowest latency doesn't seem to be chosen, nor can I configure it.

As a user I expected to be able to control this since I can select my preferred proxy in the Coder dashboard:


此 issue 未指明任何檔案、測試或進入點。先追蹤 extension 如何選取並連線至 Coder workspace proxy，然後將該行為與 Coder dashboard 中的偏好 proxy 控制項進行比較。當使用者可以選取 workspace proxy，且 extension 會使用該選取結果，包括 proxy 具有不同延遲的情況，即表示完成。

由索引模型根據 Issue 內容生成。