Create a note on a post. This operation is experimental.
Requires the `notes:write` scope.

See the [Notes guide](https://developers.buffer.com/guides/notes.md) for the complete workflow and error handling.

```graphql
mutation CreateNote {
  createCollaborationNote(input: {
    subject: { postId: "YOUR_POST_ID" }
    text: "Please review the revised caption."
    annotations: []
  }) {
    __typename
    ... on CreateCollaborationNoteSuccess {
      edge { cursor node { id text allowedActions } }
    }
    ... on MutationError { message }
  }
}
```

For a channel-less draft, replace the subject with `{ contentItemId: "YOUR_CONTENT_ITEM_ID" }`. Use a ContentItem ID, not an Idea-board ID.