Append board item journal entry

curl --request POST \
  --url https://api.wacht.dev/ai/actor-projects/{project_id}/board/items/{item_id}/journal \
  --header 'Authorization: <api-key>' \
  --header 'Content-Type: application/json' \
  --data '
{
  "summary": "<string>",
  "details": null,
  "body_markdown": "<string>",
  "attachments": {}
}
'

{
  "id": "<string>",
  "board_item_id": "<string>",
  "thread_id": "<string>",
  "execution_run_id": "<string>",
  "event_type": "<string>",
  "summary": "<string>",
  "body_markdown": "<string>",
  "details": {},
  "created_at": "2023-11-07T05:31:56Z"
}