cookie authentication for Tor

[Raimo33]

I propose using cookie authentication for the tor control connection from knots to tor-client. This way we can avoid the following lines of the .env

# Tor control credentials used internally
TOR_CONTROL_PASSWORD=your_tor_control_password
TOR_CONTROL_HASHED_PASSWORD=16:ADDBD7CF108C995F60F831F115BA5EB95322FC4645433CDEB8948A57DF

This way the .env only contains strictly the configuration options for the final user. Better UX.

This is possible only once issue #3 is implemented