Implement requireParentSpan for fs instrumentation

[unflxw]

Other OTel instrumentations (such as Mongoose) have a requireParentSpan option. When active, they will only create a span if there's already an active span in the current context that can be their span's parent -- that is, their span will never be the root span.

This could be useful in reducing noise in our users' dashboards, as users' applications and libraries often read files at points which are not already in an instrumentation context. A trace consisting only of "fs openFile" every time you boot your app is not particularly useful to the user.

[unflxw]

OTel PR: open-telemetry/opentelemetry-js-contrib#1335