fix(instrumentation-http): add server attributes after they become available

[pichlermarc]

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Which problem is this PR solving?

While reviewing #5079 I noticed that we don't set http.route and http.response.status code in the server duration metrics, so this PR addresses a few problems:

• We did not add http.route to the Span on "new" metrics
• We add the http.route only when DUPLICATE emission is turned on because
  • we also didn't add it to the Span for "new" metrics
  • but we did add it for the "old" metrics and the attribute name happens to match
• we never added the http.response.status code, because
• it is not yet determined when we add it (before the request is handled)

NOTE: skipping changelog because this is a bug in an unreleased feature

Supersedes #5079 Related to #5026

Type of change

• [x] Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

• [x] Added assertions to unit tests