Only use in-memory cache for database settings, set ttl=5 (#12166)

* Only use in-memory cache for database settings

Make necessary adjustments to monkeypatch
  as it is very vunerable to recursion
  Remove migration exception that is now redundant

Clear cache if a setting is changed

* Use dedicated middleware for setting cache stuff
  Clear cache for each request

* Add tests for in-memory cache

awx/__init__.py

@@ -78,9 +78,10 @@ def oauth2_getattribute(self, attr):
     # Custom method to override
     # oauth2_provider.settings.OAuth2ProviderSettings.__getattribute__
     from django.conf import settings
+    from oauth2_provider.settings import DEFAULTS
 
     val = None
-    if 'migrate' not in sys.argv:
+    if (isinstance(attr, str)) and (attr in DEFAULTS) and (not attr.startswith('_')):
         # certain Django OAuth Toolkit migrations actually reference
         # setting lookups for references to model classes (e.g.,
         # oauth2_settings.REFRESH_TOKEN_MODEL)