Support for API Gateway WebSocket (WS) invocation

[andyrichardson]

Hey there - first off, thanks for making this plugin!

Feature request

State machines currently cannot be not invoked by websocket events

stepFunctions:
  stateMachines:
    myMachine:
      events:
        - websocket:
            route: $connect

Note: Full reproduction here

Initially I thought this was a bug (no error during deployment) but it looks like this just isn't supported currently.

Would be nice to have event feature parity with lambda functions 🤞