Support decide shouldSample on process end

[hmleo]

In the current header sampling mechanism, the samplingResult is depend on Instrumenter.start(), such as parent or traceIdRatio.

When the samplingResult create ends, there may be an invocation exception in instrument target method, and exception is usually the information we focus on. We want to be able to find this kind of focused span during the span process and then decide whether to sample it or not.

Of course, we can also realize our demands in the tail sampling mode, but it must be 100% sampled in the head, which will cause an increase in resource consumption to a certain extent.

So, can it support decide sample on proccess end ?

[CodePrometheus]

Is there any update on this? I'd like to fix this mistake.