Add a configuration setting for the edx language cookie

CHANGELOG.md

+- Role: edxapp
+  - Add the EDXAPP_LANGUAGE_COOKIE setting
 - Role: rabbitmq
   - Upgraded to 3.6.9
   - Switched to a PPA rather than a .deb hosted in S3

playbooks/roles/edxapp/defaults/main.yml

@@ -286,6 +286,7 @@ EDXAPP_RATE_LIMITED_USER_AGENTS: []
 
 EDXAPP_LANG: 'en_US.UTF-8'
 EDXAPP_LANGUAGE_CODE : 'en'
+EDXAPP_LANGUAGE_COOKIE: 'openedx-language-preference'
 EDXAPP_TIME_ZONE: 'America/New_York'
 
 EDXAPP_LMS_DOC_LINK_BASE_URL: 'https://edx.readthedocs.io/projects/open-edx-learner-guide'
@@ -926,6 +927,7 @@ generic_env_config:  &edxapp_generic_env
   FEEDBACK_SUBMISSION_EMAIL: "{{ EDXAPP_FEEDBACK_SUBMISSION_EMAIL }}"
   TIME_ZONE: "{{ EDXAPP_TIME_ZONE }}"
   LANGUAGE_CODE: "{{ EDXAPP_LANGUAGE_CODE }}"
+  LANGUAGE_COOKIE: "{{ EDXAPP_LANGUAGE_COOKIE }}"
   MKTG_URL_LINK_MAP: "{{ EDXAPP_MKTG_URL_LINK_MAP }}"
   MKTG_URLS: "{{ EDXAPP_MKTG_URLS }}"
   SUPPORT_SITE_LINK: "{{ EDXAPP_SUPPORT_SITE_LINK }}"