cli: `call` command: This command has 2 subcommands: `make` and `receive` to make a new call or wait for one. When call is in progress, a window will be created to show incoming stream and local feedback, and a text UI is available to (un)mute audio or video, and hang up. rel 426

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