netx: investigate refraction-networking/utls (3/n)

[bassosimone]

Continues the work of #1424.

We discussed with @kelmenhorst that we want to start rewriting Web Connectivity to use parroting. We are also going to use the code in ooni/probe-cli#414 to test TLS parroting.

[bassosimone]

We did quite some testing of parroting with @kelmenhorst. We replaced the initial design of a custom HTTP transport that is able to handle both HTTP/2 and HTTP/1.1 with a simpler design where we fork net/http and we make it able to transparently handle any TLS library.

The original enhanced transport design is described at ooni/probe-cli#414.

We can consider this phase of the testing complete now.