As a follow-up to the work done in https://phabricator.wikimedia.org/T396983, we'd like to build a prototype for the labels of linked entities functionality in GraphQL on a publicly available wiki like beta or patch demo

Acceptance criteria:

• For the endpoint itself, we'll limit it to a GET item/label and a GET item/statement
• Ensure that only the labels of linked entities (statement property and statement value items) can be requested, and not everything else (for example, descriptions or subsequent statements and so on.)
• statement value types that must be supported: string values and item values
• The final endpoint will be exposed through a special page
• if possible, check if we can make it easy to try out via GraphiQL client on another special page

Task breakdown

1. create a special page that exposes a GraphQL endpoint
   • should allow for querying a single item and return its ID
   • example query: { item(id: "Q71") { id } }
2. fetching labels of the item
   • { item(id: "Q71") { labels { ar de en } } }
3. fetching statements of the item including statement property ids and labels
   • example query:

{
  item(id: "Q71") {
    statements {
      property { 
        id
        labels { en } 
      }
    }
  }
}

4. Batching to ensure that statement property labels are queried at once (possibly together with the labels of the main item)
5. Support querying statements with string values
   • filter out statements with value types we don't support
   • "type" for the value type might be a reserved keyword
   • example query:

{
  item(id: "Q71") {
    statements {
      property { 
        id
      }
      value {
        type
        content
      }
    }
  }
}

6. Support item values
7. Support labels of item values
8. GraphiQL