Allow rooms to be empty for jitsi labs

What does this mr do?

Actions taken to fix bug

Does this MR meet the acceptance criteria?

• I have added a changelog entry to reflect the significant changes I made and the bug I fixed.
• A test was created to test the bug.
• I have updated the documentation accordingly.
• I adhere to the style guide.

src/main/java/nl/tudelft/queue/dto/create/labs/CapacitySessionCreateDTO.java

@@ -67,6 +67,7 @@ public class CapacitySessionCreateDTO extends QueueSessionCreateDTO<CapacitySess
 			errors.rejectValue("capacitySessionConfig.selectionAt",
 					"Selection should be after enrolment closes");
 		}
+		nonEmpty("rooms", super.getRooms());
 	}
 
 	@Override