Add --proxy option to enable the network proxy for the http requests in the android emulator.

Is your feature request related to a problem? Please describe.
Currently, I couldn't set a network proxy for the http requests in the android emulator. I noticed that avd has this option but tns doesnt. And I did all the searching in the documents and stackoverflow and still didnt find one. Currently I am on a project that have to request facebook's api, but I am in China, I cant access those api with proxy in the android emulator, so I am stuck on it now.

Describe the solution you'd like
Add --proxy option to enable the network proxy for the http requests in the android emulator like avd -http-proxy did.

Describe alternatives you've considered
I think --proxy is the most straightforward solution, or u could add some additional file in the project to have this function.

Additional context
I think its a key function, for users in mainland China, without proxy or vpn, they cant access public api from Twitter or Facebook, so please add this function ASAP, thanks.

首先追蹤 Android 模擬器的啟動路徑和 CLI 現有的選項解析，並以所要求的 --proxy 行為和 avd -http-proxy 作為參考。完成的標準是：CLI 接受該選項，將其傳遞給模擬器的 HTTP Proxy 設定，並透過模擬器經由 Proxy 發出的請求進行驗證。