Templatize the otelhttp semconv module

[dmathieu]

So it can be reused by other instrumentation packages.

Closes #5790

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 68.6%. Comparing base (df8e435) to head (d9ef596).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #6626     +/-   ##
=======================================
- Coverage   68.6%   68.6%   -0.1%     
=======================================
  Files        200     200             
  Lines      16872   16872             
=======================================
- Hits       11585   11582      -3     
- Misses      4939    4941      +2     
- Partials     348     349      +1     

Files with missing lines	Coverage Δ
...entation/net/http/otelhttp/internal/semconv/env.go	93.3% <ø> (ø)
...ion/net/http/otelhttp/internal/semconv/httpconv.go	87.0% <ø> (ø)
...ntation/net/http/otelhttp/internal/semconv/util.go	89.4% <ø> (ø)
...tion/net/http/otelhttp/internal/semconv/v1.20.0.go	93.6% <ø> (ø)

... and 1 file with indirect coverage changes