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.

Comece rastreando o caminho de inicialização do emulador Android e a análise de opções existente da CLI, usando o comportamento solicitado de --proxy e avd -http-proxy como referência. Considera-se concluído quando a opção é aceita pela CLI, passada para a configuração de proxy HTTP do emulador e verificada com uma solicitação do emulador por meio de um proxy.