Child observation should be noop if parent is noop

[marcingrzejszczak]

If an ObservationPredicate "disables" an observation it's a NOOP observation. Now, when the child Observation is created and its parent is NOOP then we should make that observation NOOP too.

[jonatan-ivanov]

There are quite a few related issues around this:

• Provide a way to make decisions based on the parent in ObservationPredicate #3678
• Add request to Observation Context at creation to enable filtering by the request spring-projects/spring-security#12854
• Add a property to disable HTTP Observations for actuator endpoints spring-projects/spring-boot#34801
• Introduce withParentOnly for @Observed #3843
• Improve filtering out middle span by SpanExportingPredicate tracing#266

But I'm not quite sure that this behavior would be right, I think ignoring an intermediate Observation without ignoring all of the subsequent ones is a valid behavior, e.g.:

• In case of A -> B -> C, I think ignoring B but keeping C should be valid: A -> C
• In case of A -> B -> C, I think ignoring A but keeping B and C should be valid: B -> C