feat: mask out token in logging

[rapiz1]

token, default_token, local_private_key will be logged as MASKED even if it's in debug level.

like:

DEBUG rathole: Config { server: Some(ServerConfig { bind_addr: "0.0.0.0:2333", default_token: Some(MASKED), services: {"foo1": ServerServiceConfig { service_type: Tcp, name: "foo1", bind_addr: "0.0.0.0:5202", token: Some(MASKED), nodelay: None }}, transport: TransportConfig { transport_type: Noise, nodelay: false, keepalive_secs: 10, keepalive_interval: 3, tls: None, noise: Some(NoiseConfig { pattern: "Noise_NK_25519_ChaChaPoly_BLAKE2s", local_private_key: Some(MASKED), remote_public_key: None }) } }), client: None }

Resolves #128