Add WebRTC to Zinnia

[bajtos]

Allow checkers to communicate using WebSockets, see https://developer.mozilla.org/en-US/docs/Web/API/WebRTC_API

There is no Deno crate we could re-use, we have to write Deno bindings for a Rust/C++ webrtc library ourselves.

My WebRTC playground: https://github.com/bajtos/webrtc-exploration

Resources:

• https://github.com/paullouisageneau/libdatachannel
• https://www.npmjs.com/package/webrtc-polyfill
• https://crates.io/crates/webrtc
• WebRTC Integrating denoland/deno#1612
• https://github.com/oslabs-beta/sono.land
• https://github.com/WonderInventions/node-webrtc
• https://github.com/GetStream/webrtc-android
• https://github.com/sipsorcery/webrtc-interop