ENT-464 Defining ENTERPRISE_ENROLLMENT_API_URL

Now that we are accessing this variable in the context of a celery worker,
we noticed that this variable wasn't defined in all of the necessary spots.

playbooks/roles/edxapp/defaults/main.yml

@@ -1163,6 +1163,7 @@ lms_env_config:
   ENTERPRISE_COURSE_ENROLLMENT_AUDIT_MODES: "{{ EDXAPP_ENTERPRISE_COURSE_ENROLLMENT_AUDIT_MODES }}"
   PASSWORD_MIN_LENGTH: "{{ EDXAPP_PASSWORD_MIN_LENGTH }}"
   PASSWORD_MAX_LENGTH: "{{ EDXAPP_PASSWORD_MAX_LENGTH }}"
+  ENTERPRISE_ENROLLMENT_API_URL: "{{ EDXAPP_ENTERPRISE_ENROLLMENT_API_URL }}"
 
 cms_auth_config:
   <<: *edxapp_generic_auth