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.

まず、Android エミュレーターの起動経路と CLI に既存のオプション解析を追跡し、要求されている --proxy の動作と avd -http-proxy を基準にします。CLI がそのオプションを受け付け、エミュレーターの HTTP プロキシ設定に渡し、プロキシ経由のエミュレーターのリクエストで検証できれば完了です。