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/models/organization.py

@@ -95,6 +95,9 @@ class Organization(CommonModel, NotificationFieldsModel, ResourceMixin, CustomVi
     job_template_admin_role = ImplicitRoleField(
         parent_role='admin_role',
     )
+    execution_environment_admin_role = ImplicitRoleField(
+        parent_role='admin_role',
+    )
     auditor_role = ImplicitRoleField(
         parent_role='singleton:' + ROLE_SINGLETON_SYSTEM_AUDITOR,
     )