Span status from HTTP code: Do not set status message if it can be inferred

[matej-g]

Relevant specification section:

Don't set the span status description if the reason can be inferred from http.status_code.

The rationale

Although method SpanStatusFromHTTPStatusCode is not directly responsible for setting the span status code and message, many instrumentation packages depend directly on it to set the span status. This puts the burden of setting the appropriate span message on those instrumentation packages.

The change presented in this PR ensures that method SpanStatusFromHTTPStatusCode returns span status code and message which can be directly used and would adhere to the requirements, i.e. for error statuses where the reason can be inferred from http.status_code attribute, the span status message will be unset (empty).

Resolves (partially) #1376

[codecov]

Codecov Report

Merging #1681 (93fa590) into main (9c305bd) will not change coverage.
The diff coverage is 100.0%.

@@          Coverage Diff          @@
##            main   #1681   +/-   ##
=====================================
  Coverage   77.2%   77.2%           
=====================================
  Files        128     128           
  Lines       6788    6788           
=====================================
  Hits        5246    5246           
  Misses      1291    1291           
  Partials     251     251           

Impacted Files	Coverage Δ
semconv/http.go	95.2% <100.0%> (ø)