Check contracts while registering/connecting

[arthcp]

• Need to make sure contracts taken as input on socket follow proper interface.
  • Plug and Switchboard can enter the system as public inputs
  • Need to add explicit interface checks when these are added.
• Some switchboards only work for specific path.
  • Eg. NativePolygon switchboard would work only between Ethereum and Polygon.
  • But these can be registered for other paths since register function is open to public.
  • One approach is to enforce switchboard itself to send register call, take its address from msg.sender
  • And have these checks at switchboard level before call comes to socket.

[arthcp]

Flow has been changed so that only switchboards can register them selves.