example: Querying menus for themes with no menu locations

Background

If you try and query for any type of menu when building an example for some of the latest WP themes (e.g. Twenty Twenty Five) they don't have menu locations. See - https://www.wpgraphql.com/docs/menus

So the below query returns no menus

query Menu {
  menus {
    nodes {
      id
      databaseId
      name
      menuItems {
        edges {
          node {
            id
            label
            parentId
          }
        }
      }
    }
  }
}

We should look at adding examples on how a user can query menus for themes with no menu locations maybe through an example plugin in the example.

Start with the menus documentation at https://www.wpgraphql.com/docs/menus and the existing example query in this issue. Then inspect the repository's example area to determine how an example plugin can support themes without menu locations. Done means the examples demonstrate how to query menus for those themes and the documented query returns useful results.