Replace proposed-parent-id with child-id. All fields required.

[dyladan]

Updates to response header

Fixes #406, #407, #398, #437

• Remove proposed-parent-id (Discussion in Remove proposed-parent-id from response header #406)
  • /cc @adriancole
• Add child-id field
  • Pointed out by @Kanwaldeep and others that the span id of the child is required to uniquely identify a request in some support cases where multiple requests share a trace ID.
• Make all fields required (Disussion in Should response header fields be optional? #398, Encourage traceresponse to be provided even when traceparent is used #437)
  • Header itself is still optional

---

Preview | Diff

[SergeyKanzhelev]

this PR is making spec better, suggestion I added is as applicable to previous iteration. So I'm approving this PR with the comment that we may need to discuss whether we need to move soem examples to the processing non-formative section

[danielkhan]

I agree with Sergey. Let's wait for 7 days for comments.

[dyladan]

I agree with Sergey. Let's wait for 7 days for comments.

Has now been 28 days :) would still appreciate reviews from some more WG members.