title: In an AppSync @auth rule, how do I set an ownerField to a property in an array?
body: <p>Imagine I have the following AppSync GraphQL schema with a <code>User</code> type, and a <code>Post</code> type with an <code>editors</code> field set to an array of <code>User</code>s:</p>
  
  <pre><code>type User
    @model 
    @auth(rules: [
      { allow: owner }
    ])
  {
    id: ID!
    owner: String!
    username: String!
  }
  
  type Post
    @model
    @auth(rules: [
      { allow: owner },
      # Can I do this?
      # { allow: owner, ownerField: "editors.owner", operations: [update] }
    ])
  {
    id: ID!
    owner: String!
    title: String!
    content: String
    editors: [User]
  }
  </code></pre>
  
  <p>How do I create an <code>@auth</code> rule to give update permissions to the <code>User</code>s in the <code>editors</code> array?</p>