feat: Allow language preferences to be shared. (#28277)

We are planning on limiting session cookies for LMS, which
will mean that under the old cookie domain, MFEs and other
IDAs would not have access to the language preference of a user.

This moves language preference cookies to use a different setting,
which means that this cookie can be shared.

openedx/core/djangoapps/lang_pref/views.py

@@ -27,7 +27,7 @@ def update_session_language(request):
         response.set_cookie(
             settings.LANGUAGE_COOKIE,
             language,
-            domain=settings.SESSION_COOKIE_DOMAIN,
+            domain=settings.SHARED_COOKIE_DOMAIN,
             max_age=COOKIE_DURATION,
             secure=request.is_secure(),
         )