Changes to GET /api/availability

added the new optional query request parameter exam_room

added the non-success response with the status 400

added the non-success response with the status 401

added the non-success response with the status 403

added the non-success response with the status 404

added the non-success response with the status 405

added the non-success response with the status 500

added the success response with the status 200