Rename to not have file extension

As this is what apple need. Also make the docker container serve
it with the right content type.

config/nginx.conf

@@ -21,5 +21,9 @@ server {
         expires 1w;
         add_header Cache-Control "public, no-transform";
     }
+
+    location /apple-app-site-association {
+        default_type application/json;
+    }
 }