Evaluate using Mockttp instead of mitmproxy

[baltpeter]

Mockttp is the intercepting proxy at the core of HTTP Toolkit, and, as far as I can tell, the one major alternative to mitmproxy. It might be worth evaluating using that instead. Potential benefits I can see:

• It's written in TypeScript instead of Python, meaning we would be able to control it directly from our code instead of having to handle a Python process.
• They have invested effort into defeating TLS fingerprinting, which makes it a lot harder for apps to detect the proxy.
• HTTP Toolkit has a native HAR export which we might also be able to use. mitmproxy only has a community-contributed addon for that.

[baltpeter]

Also worth noting: HTTP Toolkit may soon have support for intercepting traffic from individual apps using Frida.