Use semconv migration package for httptrace

[dmathieu]

This uses the semconv internal package within httptrace, so we can migrate to stable HTTP attributes.

Closes #6637

[codecov]

Codecov Report

Attention: Patch coverage is 86.70520% with 115 lines in your changes missing coverage. Please review.

Project coverage is 74.5%. Comparing base (d5cac4a) to head (c3b27e0).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
...tptrace/otelhttptrace/internal/semconv/httpconv.go	86.0%	42 Missing and 15 partials ⚠️
...ttptrace/otelhttptrace/internal/semconv/v1.20.0.go	87.7%	15 Missing and 7 partials ⚠️
...tp/httptrace/otelhttptrace/internal/semconv/env.go	87.7%	17 Missing and 1 partial ⚠️
...m/gorilla/mux/otelmux/internal/semconv/httpconv.go	57.1%	6 Missing ⚠️
...p/httptrace/otelhttptrace/internal/semconv/util.go	89.4%	4 Missing and 2 partials ⚠️
...ion/net/http/otelhttp/internal/semconv/httpconv.go	57.1%	6 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #6720     +/-   ##
=======================================
+ Coverage   73.9%   74.5%   +0.6%     
=======================================
  Files        195     199      +4     
  Lines      16671   17529    +858     
=======================================
+ Hits       12332   13075    +743     
- Misses      3980    4070     +90     
- Partials     359     384     +25     

Files with missing lines	Coverage Δ
...ub.com/gorilla/mux/otelmux/internal/semconv/env.go	90.4% <100.0%> (+0.8%)	⬆️
...om/gorilla/mux/otelmux/internal/semconv/v1.20.0.go	88.8% <100.0%> (+0.3%)	⬆️
...on/net/http/httptrace/otelhttptrace/clienttrace.go	79.5% <100.0%> (+<0.1%)	⬆️
...tion/net/http/httptrace/otelhttptrace/httptrace.go	100.0% <100.0%> (ø)
...entation/net/http/otelhttp/internal/semconv/env.go	93.8% <100.0%> (+0.5%)	⬆️
...tion/net/http/otelhttp/internal/semconv/v1.20.0.go	93.8% <100.0%> (+0.2%)	⬆️
...m/gorilla/mux/otelmux/internal/semconv/httpconv.go	86.0% <57.1%> (-1.1%)	⬇️
...p/httptrace/otelhttptrace/internal/semconv/util.go	89.4% <89.4%> (ø)
...ion/net/http/otelhttp/internal/semconv/httpconv.go	86.0% <57.1%> (-1.1%)	⬇️
...tp/httptrace/otelhttptrace/internal/semconv/env.go	87.7% <87.7%> (ø)
... and 2 more

... and 1 file with indirect coverage changes