Add in more model changes around execution environments

- a new unique name field to EE
- a new configure-Tower-in-Tower setting DEFAULT_EXECUTION_ENVIRONMENT
- an Org-level execution_environment_admin_role
- a default_environment field on Project
- a new Container Registry credential type
- order EEs by reverse of the created timestamp
- a method to resolve which EE to use on jobs

awx/main/tests/functional/test_credential.py

@@ -90,6 +90,7 @@ def test_default_cred_types():
         'kubernetes_bearer_token',
         'net',
         'openstack',
+        'registry',
         'rhv',
         'satellite6',
         'scm',