cli (call, file), frontends: implement webRTC data channel transfer: - file send/receive commands now supports webRTC transfer. In `send` command, the `--webrtc` flags is currenty used to activate it. - WebRTC related code have been factorized and moved to `libervia.frontends.tools.webrtc*` modules. rel 442

this certificates are used to enable TLS during tests. Those must be the same as in
backend_e2e (they are generated there)