fix: include credentials when cookie across subdomains

 This URL of fetching guest_token is always LMS_ROOT_URL, however
 in case multisite is being used the guest could be in a different
 url. This change ensure that cookie is being sent if the other
 site is a subdomain or shares parent domain with LMS_URL_ROOT

 This might be realted to openedx/tutor-contrib-aspects/issues/925

platform_plugin_aspects/static/js/embed_dashboard.js

@@ -30,6 +30,7 @@ async function fetchGuestToken() {
     headers: {
       "X-CSRFToken": getCookie("csrftoken"),
     },
+    credentials: 'include',
     body: body,
   });