Add new commands to support watching for port changes

[Xayton]

Describe the request

New commands:

• startwatchports: starts watching and returns multiple add events (corresponding to all the known ports at that time)
• stopwatchports

When the WebSocket connection is closed by the client, the agent will automatically stop sending events and eventually stop watching for port changes (this is an internal implementation detail).

At the start of the communication, the watch functionality is stopped, and has to be started manually with a startwatchports.

If the agent is already sending watchport events, a startwatchports will not do anything. Same for the other way around with stopwatchports.

Result message:

{
  "message_type": "watchportevent"
  "message_data": 
  {
    "eventType": "add",
    "port": {
      "address": "/dev/ttyACM0",
      "label": "/dev/ttyACM0",
      "protocol": "serial",
      "protocol_label": "Serial Port (USB)",
      "properties": {
        "pid": "0x0070",
        "serialNumber": "3485187AA318",
        "vid": "0x2341"
      },
      "hardware_id": "3485187AA318"
    }
  }
}

Note: multiple port additions or removals would be sent using multiple watchportevent messages.

Describe the current behavior

Currently the Agent does not support watch functionality.

Arduino Create Agent version

1.3.8

Operating system

N/A

Operating system version

N/A

Browser

N/A

Browser version

N/A

Additional context

No response

Issue checklist

• I searched for previous requests in the issue tracker
• I verified the feature was still missing when using the latest version
• My request contains all necessary details