Implement logs model using Elasticsearch

- Implement logs model using Elasticsearch with tests
- Implement transition model using both elasticsearch and database model
- Add LOGS_MODEL configuration to choose which to use.

Co-authored-by: Sida Chen <sidchen@redhat.com>
Co-authored-by: Kenny Lee Sin Cheong <kenny.lee@redhat.com>

test/registry/registry_tests.py

@@ -243,6 +243,7 @@ def add_token(_, executor):
   return ('$token', executor.add_token().text)
 
 
+# TODO(sidchen): Test logging to elastic search log model.
 @pytest.mark.parametrize('credentials, namespace, expected_performer', [
   (('devtable', 'password'), 'devtable', 'devtable'),
   (add_robot, 'buynlarge', 'buynlarge+ownerbot'),