Support for HTTPS proxy configurations

[stevejpurves]

It is not possible to use the CLI on networks that enforce a strict proxy policy for internet access.

Proposal

Enable proxy based access through by using the https-proxy-agent middleware with node-fetch and allowing users to specify their proxy configuration string via an environment variable HTTPS_PROXY.

We'd need to ensure that all fetch calls receive the proxy configuration, so could consider an extension to the session object to provide easy access to an appropriately configured call to fetch.

Additional notes

e.g.

const fetch = require('node-fetch');
const HttpsProxyAgent = require('https-proxy-agent');
const Http = require('https');

const url = "https://www.google.com/images/branding/googlelogo/1x/googlelogo_color_272x92dp.png";
const proxyUrl = process.env.HTTPS_PROXY;

const options = {
    agent: HttpsProxyAgent(proxyUrl)
};

const response = await fetch(url, options);