instrumentation: use parent-based sampling.

If we have a tracing enabled, we always want to sample
spans whenever
  - our own probabilistic sampler says so, or
  - we have a parent span and it is being sampled

Therefore use a parent-based probabilistic sampler instead
of just a probabilistic one.

Signed-off-by: Krisztian Litkey <[email protected]>

pkg/instrumentation/tracing/tracing.go

@@ -152,7 +152,7 @@ func (t *tracing) start(options ...Option) error {
 			sdktrace.NewBatchSpanProcessor(exporter),
 		),
 		sdktrace.WithSampler(
-			sdktrace.TraceIDRatioBased(t.sampling),
+			sdktrace.ParentBased(sdktrace.TraceIDRatioBased(t.sampling)),
 		),
 	)