feat: Signals support

[x1unix]

Support signals and slots for actions.

Example:

tasks:
  # Task to debug task runner
  test:
    inputs:
      # Test message content
      message:
        type: string

      # Signal name
      signal:
        type: string
        default: mysignal

    steps:
      - action: debug/signal
        with:
          signal: ${{inputs.signal}}
        on:
          mysignal:
            - action: debug/echo
              with:
                message: "message: ${{inputs.message}}, data: ${{toJSON(event)}}"
          error:
            - action: debug/echo
              with:
                message: Error happened