Allow users to control child trace span creation

[andreasohlund]

Describe the feature.

Is your feature related to a problem? Please describe.

Currently a child span is always created for the incoming message if a traceparent header is present on the incoming message. To avoid too large traces it can be helpful for the user to control this and eg only use a child trace span based on some convention on the incoming message

Describe the requested feature

Describe alternatives you've considered

Additional Context

No response