Use HTTPS in local development

[eatyourgreens]

• Install selfsigned.
• Run the proxy server with a self-signed certificate in development mode.

[eatyourgreens]

npm start runs in production mode, not development, so the proxy still runs with HTTP. See #126.

[shaunanoordin]

PR Review

Affects: proxy server (local development only)

This PR adds self-signed certs to the Proxy Server for local development.

• Code read looks pretty straightforward
• Running npm run proxy-server seems to load the Proxy on local with no issues (though there are a bunch of other variables required - e.g. current URL for MS ML service) that would be required for full testing

Testing

In short, try to get the Proxy Server to show an example HTML webpage.

1. Setup: create an .env file with TARGETS=https://example.com
2. Run npm run proxy-server
3. Open https://local.zooniverse.org:3666/?url=https://example.com/index.html in your browser
4. The content should pretty much match https://example.com/index.html

Status

Looks good, but there's one change required to get this PR merged: changing NODE_ENV to process.env.NODE_ENV