Resolve "Lab should remain visible and serviceable for a bit after the official closing time of the lab"

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Closes #485 (closed), #494 (closed), #417 (closed)

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

@@ -23,6 +23,9 @@ import java.util.Map;
 import java.util.Set;
 import java.util.stream.Collectors;
 
+import javax.validation.constraints.Max;
+import javax.validation.constraints.Min;
+
 import lombok.*;
 import lombok.experimental.SuperBuilder;
 import nl.tudelft.labracore.api.dto.AssignmentIdDTO;
@@ -41,6 +44,10 @@ import nl.tudelft.queue.model.labs.Lab;
 public abstract class LabCreateDTO<D extends Lab> extends QueueSessionCreateDTO<D> {
 	private CommunicationMethod communicationMethod;
 
+	@Min(0)
+	@Max(180)
+	private Integer eolGracePeriod;
+
 	@Builder.Default
 	private Map<Long, Set<RequestType>> requestTypes = new HashMap<>();