[Backend] Create API endpoint to mark/unmark a question as resolved

[SubtoFelix]

Estimated Effort: 5-6 hours
Dependencies: Issue#2 (Database changes)
Acceptance Criteria: API endpoint exists for the "resolved" status, API returns appropriate success/error responses.

[Misterurias]

Used a curl command to test api endpoint:

(venv) ➜ nodebb-s25-cheese git:(feature-resolved-field) ✗ curl -X PUT "http://localhost:4567/api/topics/1/resolved?_uid=1"
-H "Content-Type: application/json"
-H "Authorization: Bearer API_TOKEN"
-d '{"resolved": true}'

{"message":"Topic resolved status updated","tid":"1","resolved":true}%

API_TOKEN must be created via the api page: http://localhost:4567/admin/settings/api