fix: allow active spans to be passed in as an option

[mrstork]

This allows an active span to be passed in allowing custom attributes to be set on spans before they are closed

Alternative solutions considered before settling on this one:

• Passing in extra attributes as options: falls short when the attributes need to be set before vs after the blob request. Quickly calls out for some sort of beforeAttributes and afterAttributes pattern which feels quite messy.
• Computed attributes: gets messy real fast and there's a high chance of causing a promise loop
• Handing off request completion or span completion to the consumer: leaky abstraction - the purpose of the api is blobs not traces

[mrstork]

Needed to support import from @netlify/otel/opentelemetry