feat: add plugin slot

[ccantillo]

Description

This PR adds an example configuration demonstrating how to use the Course Outline Header Actions plugin slot (org.openedx.frontend.authoring.course_outline_header_actions.v1) in the frontend-app-authoring MFE.

What's Changed

• Added example-course-outline-header-actions.config.jsx - A working example that demonstrates how to:
  • Insert a custom button into the Course Outline header actions area
  • Fetch data from the Course Team API using the correct STUDIO_BASE_URL
  • Get the authenticated user's role (instructor, staff, etc.)
  • Display dynamic content based on API responses
  • Handle loading and error states

Key Implementation Details

• Uses getConfig().STUDIO_BASE_URL to ensure API calls go to the correct backend (studio endpoint) rather than the MFE frontend