Add serialization of requests of a lab into CSV

Add the serialization of a List of Requests into a CSV in the helper class LabCsvHelper. Add a LabController endpoint for downloading this export.

Closes #302 (closed)

src/main/java/nl/tudelft/ewi/queue/controller/LabController.java

@@ -467,6 +467,7 @@ public class LabController {
 	 * @throws JsonProcessingException when something goes wrong processing requests.
 	 */
 	@GetMapping("/lab/{id}/export")
+	@PreAuthorize("@permissionService.canExportLab(principal, id)")
 	public ResponseEntity<Resource> downloadLabExport(@PathVariable Long id) throws JsonProcessingException {
 		Lab lab = labService.getLab(id);