Support proxy server configuration

Hi SWA-Team,

first! Great Tool! it works very well from my developer machine outside our company network.

Our CI/CD tool (jenkins) is part of the company network secured by a proxy server.

We are not able to fetch the https://swalocaldeploy.azureedge.net/downloads/versions.json file from the corporate network. (./src/core/deploy-client.ts:151)

Describe the solution you'd like
It would be great to have some proxy options to handle the outgoing requests. There is a nice package to add a proxy agent to node-fetch.

https-proxy-agent

Some cli parameters to setup the proxy configuration would be nice solution.

Describe alternatives you've considered

Does the docker-way do the trick? Does the docker image contain the StaticSitesClient and this step could skipped?

Thanks a lot for this great cli tool.

But for now, we cant use it