fix(custom-views): Allow view's query field to be empty (#76569)

Views containing an empty query failed validation, and I can't think of
a reason to disallow empty queries.

src/sentry/api/serializers/rest_framework/groupsearchview.py

@@ -20,7 +20,7 @@ class GroupSearchViewValidatorResponse(TypedDict):
 class ViewValidator(serializers.Serializer):
  id = serializers.CharField(required=False)
  name = serializers.CharField(required=True)
- query = serializers.CharField(required=True)
+ query = serializers.CharField(required=True, allow_blank=True)
  querySort = serializers.ChoiceField(
  choices=SortOptions.as_choices(), default=SortOptions.DATE, required=False
  )