Create message

curl --request POST \
  --url https://api.campsite.com/v2/threads/{thread_id}/messages \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --data '{
  "content_markdown": "<string>",
  "parent_id": "<string>"
}'

{
  "id": "<string>",
  "content": "<string>",
  "created_at": "<string>",
  "updated_at": "<string>",
  "parent_id": "<string>",
  "thread_id": "<string>",
  "author": {
    "avatar_urls": {
      "xs": "<string>",
      "sm": "<string>",
      "base": "<string>",
      "lg": "<string>",
      "xl": "<string>",
      "xxl": "<string>"
    },
    "name": "<string>",
    "id": "<string>",
    "type": "app"
  }
}