Aspnetcore: [Epic] ASP.NET Core should support distributed tracing

[anurse]

We should provide integration with distributed tracing work going on throughout .NET.

Child Items:

• [x] https://github.com/aspnet/AspNetCore/issues/5926 Ambient distributed tracing context
• [x] https://github.com/aspnet/AspNetCore/issues/5925 Support W3C format for distributed trace context propagation
• [x] https://github.com/aspnet/AspNetCore/issues/5918 Parent Request Id is mislabeled as Correlation Id in log scope
• https://github.com/aspnet/AspNetCore/issues/5927 Use TraceIdentifier of HttpContext as a span in W3C when possible cut from 3.0
• https://github.com/aspnet/AspNetCore/issues/5914 Add a way to configure the IHttpRequestIdentifierFeature to read a configurable header cut from 3.0
• https://github.com/aspnet/AspNetCore/issues/5928 Serialize response context as a response header cut from 3.0

[anurse]

Note: we don't really have resources allocated to this right now.

cc @glennc

[davidfowl]

I don't think we need to do all of these as part of the epic. We should meet with @lmolkova next week and narrow down the items to the MVP.