update graphql playground config

api/src/graphql/handler.rs

···
 
       const fetcher = createGraphiQLFetcher({{
         url: '/graphql',
+        subscriptionUrl: '/graphql/ws?slice={}',
         headers: {{
           'X-Slice-Uri': '{}'
         }}
···
     </div>
   </body>
 </html>"#,
+        slice_uri.replace("'", "\\'").replace("\"", "\\\""),
         slice_uri.replace("'", "\\'").replace("\"", "\\\"")
     );