Description

Update the API:

• extract_or_create_span always returns a span, either the extracted one or a new span if the extraction fail.
• override_sampling_priority accepts SamplingPriority.

Motivation

create_span always returns a span, while extract_span may or may not return a span. Logically, one can think the behavior of extract_or_create_span should first attempt to extract_span, and if the extraction fails, it should then call create_span. At least, that's what the name of the function suggest and I think the desired behavior.

The other one is for simplicity's sake.