add report_configs_by_domain despite being unused

If in the event someone wanted to add this view to production code,
it is unreasonable to expect them to know to add it here as well.
This has the added benefit of making the view useful in the context
of a django shell.

corehq/apps/cachehq/cachemodels.py

@@ -20,4 +20,5 @@ class UserReportsDataSourceCache(GenerationCache):
         'userreports/data_sources_by_build_info',
         'userreports/data_sources_by_last_modified',
         'userreports/report_configs_by_data_source',
+        'userreports/report_configs_by_domain',
     ]