feat: add frontend-plugin-framework slots (#545)

Add the following `frontend-plugin-framework` slots:
* `logo_slot`
* `desktop_main_menu_slot`
* `desktop_secondary_menu_slot`
* `mobile_main_menu_slot`
* `course_info_slot`
* `learning_help_slot`
* `desktop_logged_out_items_slot`
* `mobile_logged_out_items_slot`
* `mobile_user_menu_slot`
* `desktop_user_menu_slot`
* `learning_user_menu_slot`
* `learning_logged_out_items_slot`
* `desktop_header_slot`

src/learning-header/LearningHeaderHelpLink.jsx

@@ -0,0 +1,14 @@
+import React from 'react';
+
+import { getConfig } from '@edx/frontend-platform';
+import { useIntl } from '@edx/frontend-platform/i18n';
+import messages from './messages';
+
+const LearningHeaderHelpLink = () => {
+  const intl = useIntl();
+  return (
+    <a className="text-gray-700" href={`${getConfig().SUPPORT_URL}`}>{intl.formatMessage(messages.help)}</a>
+  );
+};
+
+export default LearningHeaderHelpLink;