addOptions() {
    return {
      node: 'paragraph',
      notAfter: ['paragraph'],
    }
  }
Extension based on:
- https://github.com/ueberdosis/tiptap/blob/v1/packages/tiptap-extensions/src/extensions/TrailingNode.js
- https://github.com/remirror/remirror/blob/e0f1bec4a1e8073ce8f5500d62193e52321155b9/packages/prosemirror-trailing-node/src/trailing-node-plugin.ts