Feature/endorse backend

[Q2L2]

• Implemented the backend for the endorse feature for issues Add a visual indicator showing the endorsement status. #26 and Restrict the endorse feature to the course instructors only. #27. This includes implementing a green badge visual indicator on the main page, the toggle logic, the set state function, routing the frontend and the backend via API end points.
• The feature Endorse Post feature is valuable for instructors to highlight certain posts as valuable for the class to look on the Q&A forum page.
• The changes added include implementing functions such as ThreadTools.setEndorsedState(), toggleEndorse(), topicsAPI.endorse() and topicsAPI.unendorse() and required API endpoints to enable the frontend to send requests to the backend and receive responses .
• Tested the backend implementations by running NodeBB locally and clicked on the Endorse Post button to trigger the UI, ensuring that the button toggles correctly, the displayed messages are visible, the visual indicator is set and the correct states are saved upon refreshing the page.