declarative configuration : inferred spans enhancements

[SylvainJuge]

Inferred spans is already available in upstream contrib, with some support of declarative configration.

There are however a few things that would be simpler to enhance/fix before we provide declarative configuration support for it in EDOT as it would otherwise become breaking changes.

• configuration is using durations in "human-friendly" form, and should switch to use milliseconds to align to declarative configuration for consistency.
• we should make the included_classes and excluded_classes rely on the common IncludeExcludePredicate implementation for consistency on include/exclude patterns
• we need to check if the parent_override_handler could be hidden from the user, for example by adding the span links optionally through a boolean option rather than having to provide an implementation class name.