Split `enforceTor` into `tor.proxy` and `tor.enforce`.
By enabling `tor.proxy` without `tor.enforce`, a service can accept
incoming clearnet connections.
E.g., this allows setting up a Tor-proxied bitcoind node that accepts
RPC connections from LAN.
Move 'enforceTor' and onion-service definitions from secure-node.nix.
Use the onionServices module to define onion services.
Onion services now automatically work for services that bind to an INADDR_ANY (`0.0.0.0`) address.