Add property to prevent observations starting with a prefix

For example, setting management.observations.enable.denied.prefix=false
will prevent all observations starting with 'denied.prefix'

Closes gh-34802

spring-boot-project/spring-boot-docs/src/main/java/org/springframework/boot/docs/actuator/observability/preventingobservations/MyObservationPredicate.java

@@ -26,7 +26,7 @@ class MyObservationPredicate implements ObservationPredicate {
 
 	@Override
 	public boolean test(String name, Context context) {
-		return !name.startsWith("denied.prefix.");
+		return !name.contains("denied");
 	}
 
 }