Make group and project dropdowns mutually exclusive for selection

app/assets/javascripts/pages/dashboard/todos/index/todos.js

@@ -55,7 +55,16 @@ export default class Todos {
         filterable: searchFields ? true : false,
         search: { fields: searchFields },
         data: $dropdown.data('data'),
-        clicked: () => $dropdown.closest('form.filter-form').submit(),
+        clicked: () => {
+          const $formEl = $dropdown.closest('form.filter-form');
+          const mutexDropdowns = {
+            group_id: 'project_id',
+            project_id: 'group_id',
+          };
+
+          $formEl.find(`input[name="${mutexDropdowns[fieldName]}"]`).remove();
+          $formEl.submit();
+        },
       });
     }
   }