Improve instrumented methods returning Futures

[schlosna]

What happened?

Instrumenting methods that return Future, ListenableFuture, or CompletableFuture provide somewhat misleading metrics as it is simply the time to return the future itself, not for the future to complete. A common case is Conjure’s async endpoints that return ListenableFutures

What did you want to happen?

We may want to consider tracking success/failure via completion of the future similar to https://github.com/palantir/tracing-java/blob/af0c1272342876fc435d5f12a59b8295fe066069/tracing/src/main/java/com/palantir/tracing/Tracers.java#L194-L238

[schlosna]

@felixdesouza recently pushed similar changes to atlasdb in palantir/atlasdb#4661 specifically TaggedMetricsInvocationEventHandler

Also linking @ellisjoe 's unmerged PR #181 from a while back.

@felixdesouza and @carterkozak curious if this is something you have cycles to push over the finish line.