feat: added support for metadata.displayName for searches

graph/loaders/users.js

@@ -110,6 +110,13 @@ const getUsersByQuery = async (
               },
             },
           },
+
+          // Search by the displayName metadata field.
+          {
+            'metadata.displayName': {
+              $regex,
+            },
+          },
         ],
       });
     }

models/schema/user.js

@@ -235,6 +235,15 @@ User.index({
   created_at: -1,
 });
 
+User.index(
+  {
+    'metadata.displayName': 1,
+  },
+  {
+    sparse: true,
+  }
+);
+
 // This query is executed often, to count the number of flagged accounts with
 // usernames.
 User.index({