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/settings/defaults.py

@@ -175,6 +175,7 @@ REMOTE_HOST_HEADERS = ['REMOTE_ADDR', 'REMOTE_HOST']
 PROXY_IP_ALLOWED_LIST = []
 
 CUSTOM_VENV_PATHS = []
+DEFAULT_EXECUTION_ENVIRONMENT = None
 
 # Note: This setting may be overridden by database settings.
 STDOUT_MAX_BYTES_DISPLAY = 1048576