feat: Add redirect to enterprise learner dashboard (#1251)

When a learner tries to load the B2C course page for a course that
starts in the future (error_code="course_not_started"), normally the
learning MFE automatically redirects to the B2C dashboard.  This change
supports an alternate error_code "course_not_started_enterprise_learner"
to trigger an alternative redirect to the B2B (enterprise) learner
dashboard.

This does two main things:

1. When the course metadata API response indicates
   course_access.error_code = "course_not_started_enterprise_learner"
   then redirect to "/redirect/enterprise-learner-dashboard".
2. When the top-level router matches path "/redirect/enterprise-learner-dashboard"
   then redirec to to the value of config `ENTERPRISE_LEARNER_PORTAL_URL`.

ENT-8078

src/shared/access.js

@@ -15,6 +15,9 @@ export function getAccessDeniedRedirectUrl(courseId, activeTabSlug, courseAccess
       const startDate = (new Intl.DateTimeFormat(getLocale())).format(new Date(start));
       url = `/redirect/dashboard?notlive=${startDate}`;
       break;
+    case 'course_not_started_enterprise_learner':
+      url = '/redirect/enterprise-learner-dashboard';
+      break;
     case 'survey_required':
       url = `/redirect/survey/${courseId}`;
       break;