Send a generic status response if the domain is not a valid proxy

[lhridder]

Describe the solution you'd like It would be useful to have a global config where you can specify what status response should be sent if a client tries to connect to an invalid proxy.

Example/default config:

"invalidProxy": {
    "versionName": "infrared",
    "protocolNumber": 1,
    "motd": "There is no proxy associated with this domain. Please check your configuration."
  }

Example server list view:

[lhridder]

Example: https://github.com/lhridder/infrared/commit/3d2ee256e6e6f9f93654064d1e60a3d82bc7e31c