title: How does one access custom fileds in an ACF relation field in GraphQL?
body: <p>I'm using Gatsby.js with the WP API. Typically you can use GraphiQL to mess with queries and the autocomplete will help answer questions like this. But I think either the utility didn't factor this level of inception or I'm not using graphQL correctly...</p>
  
  <pre><code>  query workInnerPageQuery{
      wordpressPage(id: { eq: "e52ad032-9468-5826-9320-a22da5b1e0c9" }) {
        id
        title
        acf{
          case_studies{ // this is a relation field
            post_title
            post_name
            --- how do you get an ACF field here?
          }
        }
      }
    }
  </code></pre>
  
  <p>I have a custom field "subtitle" for example. This doesn't work...</p>
  
  <pre><code>  acf{
      case_studies{
        post_title
        post_name
        acf{
          subtitle
        }
      }
    }
  </code></pre>
  
  <p>Seeing as subtitle is an acf field of the post type "case_study" which is a relation item on this specific page... how does one access an ACF field within an ACF field?</p>
  
  <p>Has anyone else had to figure this out?</p>