Resolve "Indicate an active filter"

What does this mr do?

Add an indicator to show the number of filters being active.

Screenshots

before

after

Does this MR meet the acceptance criteria?

• I have added a changelog entry to reflect the significant changes I made.
• Tests were created to test the feature.
• I have updated the documentation accordingly.
• I adhere to the style guide. Closes #503 (closed)

src/main/java/nl/tudelft/queue/dto/util/RequestTableFilterDTO.java

@@ -20,6 +20,7 @@ package nl.tudelft.queue.dto.util;
 import java.io.Serializable;
 import java.util.HashSet;
 import java.util.Set;
+import java.util.stream.Stream;
 
 import javax.validation.constraints.NotNull;
 
@@ -50,10 +51,27 @@ public class RequestTableFilterDTO extends Validated implements Serializable {
 	private Set<RequestType> requestTypes = new HashSet<>();
 
 	public boolean isEmpty() {
-		return labs.isEmpty() &&
-				assignments.isEmpty() && rooms.isEmpty() &&
-				assigned.isEmpty() && requestStatuses.isEmpty() &&
-				requestTypes.isEmpty();
+		return getAllFiltersAsStream().filter(s -> !s.isEmpty()).toList().isEmpty();
+	}
+
+	/**
+	 * Counts the number of filters which are active.
+	 *
+	 * @return The number of lists which contain at least 1 element to filter on.
+	 */
+	public long countActiveFilters() {
+		return Stream.of(labs, assigned, rooms, assigned, assignments, requestStatuses,
+				requestTypes).filter(s -> !s.isEmpty()).count();
+	}
+
+	/**
+	 * Get all existing filters as a stream.
+	 *
+	 * @return A stream of Sets.
+	 */
+	private Stream<Set<?>> getAllFiltersAsStream() {
+		return Stream.of(labs, assigned, rooms, assigned, assignments, requestStatuses,
+				requestTypes);
 	}
 
 	@Override