Drop support for test mode?

[taylordowns2000]

We'd provided an option for test mode which would try to intercept http requests made with request (so... lots of language-packages until recently) but that no longer works with axios and request is deprecated. We had used https://www.npmjs.com/package/mitm , but after a hard look it feels like this really shouldn't be the responsibility of core.

I'd move to drop support for test mode and let folks set up their own proxies with axios if they really want. Thoughts @stuartc , @lakhassane , @chaiwa-berian ?