Send the agent a message

Asks the agent for work the way a message in the messenger does. Omit `conversationID` to open a new conversation; the response carries the one it opened.

curl -X POST "https://example.com/agent/messages" \  -H "Content-Type: application/json" \  -d '{    "message": "string"  }'

{  "conversationID": "string",  "messageID": "string",  "result": null}