Change retired config username/email values to be more explicit.

CHANGELOG.md

+- Role: edxapp
+  - Changed `EDXAPP_RETIRED_USERNAME_FMT` to `EDXAPP_RETIRED_USERNAME_PREFIX`. Changed/split `EDXAPP_RETIRED_EMAIL_FMT` to be `EDXAPP_RETIRED_EMAIL_PREFIX` and `EDXAPP_RETIRED_EMAIL_DOMAIN`.
+
 - Role xqueue
   - Removed RabbitMQ in earlier changes in XQueue itself, we don't need any of the configuration
     XQUEUE_RABBITMQ_USER XQUEUE_RABBITMQ_PASS XQUEUE_RABBITMQ_VHOST XQUEUE_RABBITMQ_HOSTNAME 

playbooks/roles/edxapp/defaults/main.yml

@@ -721,8 +721,9 @@ EDXAPP_PROCTORING_BACKEND_PROVIDER:
   class: 'edx_proctoring.backends.null.NullBackendProvider'
   options: {}
 
-EDXAPP_RETIRED_USERNAME_FMT: "retired__user_{}"
-EDXAPP_RETIRED_EMAIL_FMT: "retired__user_{}@retired.invalid"
+EDXAPP_RETIRED_USERNAME_PREFIX: "retired__user_"
+EDXAPP_RETIRED_EMAIL_PREFIX: "retired__user_"
+EDXAPP_RETIRED_EMAIL_DOMAIN: "retired.invalid"
 EDXAPP_RETIRED_USER_SALTS:
   - "OVERRIDE ME WITH A RANDOM VALUE"
   - "ROTATE SALTS BY APPENDING NEW VALUES"
@@ -1238,8 +1239,9 @@ generic_env_config:  &edxapp_generic_env
   EXTRA_MIDDLEWARE_CLASSES: "{{ EDXAPP_EXTRA_MIDDLEWARE_CLASSES }}"
   MAINTENANCE_BANNER_TEXT: "{{ EDXAPP_MAINTENANCE_BANNER_TEXT }}"
 
-  RETIRED_USERNAME_FMT: "{{ EDXAPP_RETIRED_USERNAME_FMT }}"
-  RETIRED_EMAIL_FMT: "{{ EDXAPP_RETIRED_EMAIL_FMT }}"
+  RETIRED_USERNAME_PREFIX: "{{ EDXAPP_RETIRED_USERNAME_PREFIX }}"
+  RETIRED_EMAIL_PREFIX: "{{ EDXAPP_RETIRED_EMAIL_PREFIX }}"
+  RETIRED_EMAIL_DOMAIN: "{{ EDXAPP_RETIRED_EMAIL_DOMAIN }}"
   RETIRED_USER_SALTS: "{{ EDXAPP_RETIRED_USER_SALTS }}"
   RETIREMENT_SERVICE_WORKER_USERNAME: "{{ EDXAPP_RETIREMENT_SERVICE_WORKER_USERNAME }}"