Migrate to semconv for otelmux and implement the package in tracing

[martinyonatann]

This PR updates the otelmux package by introducing the semconv package and using it with tracing only. It also updates the template and refines the gen.go in otelhttp to reflect the changes made in the template.

This PR addresses feedback provided in #6648

[martinyonatann]

I had to delete the semconv gen.go file because when running make precommit, the otelhttp library was re-imported, which broke the generated code.

[martinyonatann]

I had to delete the semconv gen.go file because when running make precommit, the otelhttp library was re-imported, which broke the generated code.

Solved by adding a parameter in the template.

[dmathieu]

Thank you for the template fix. I've extracted it into another PR, so other instrumentations aren't blocked by this one. #6663

[dmathieu]

This will need a changelog entry.

[codecov]

Codecov Report

Attention: Patch coverage is 87.91774% with 94 lines in your changes missing coverage. Please review.

Project coverage is 73.8%. Comparing base (bf0e3dd) to head (94b748b).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
...m/gorilla/mux/otelmux/internal/semconv/httpconv.go	87.0%	36 Missing and 15 partials ⚠️
...om/gorilla/mux/otelmux/internal/semconv/v1.20.0.go	88.4%	13 Missing and 7 partials ⚠️
...ub.com/gorilla/mux/otelmux/internal/semconv/env.go	89.6%	11 Missing and 3 partials ⚠️
...b.com/gorilla/mux/otelmux/internal/semconv/util.go	89.4%	4 Missing and 2 partials ⚠️
...trumentation/github.com/gorilla/mux/otelmux/mux.go	84.2%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #6652     +/-   ##
=======================================
+ Coverage   73.1%   73.8%   +0.7%     
=======================================
  Files        191     195      +4     
  Lines      15867   16627    +760     
=======================================
+ Hits       11607   12285    +678     
- Misses      3925    3982     +57     
- Partials     335     360     +25     

Files with missing lines	Coverage Δ
...trumentation/github.com/gorilla/mux/otelmux/mux.go	94.0% <84.2%> (+9.0%)	⬆️
...b.com/gorilla/mux/otelmux/internal/semconv/util.go	89.4% <89.4%> (ø)
...ub.com/gorilla/mux/otelmux/internal/semconv/env.go	89.6% <89.6%> (ø)
...om/gorilla/mux/otelmux/internal/semconv/v1.20.0.go	88.4% <88.4%> (ø)
...m/gorilla/mux/otelmux/internal/semconv/httpconv.go	87.0% <87.0%> (ø)

[akats7]

Will review after body wrapper is merged/included

[dmathieu]

Can you fix the conflicts that were introduced with the merge of your other PR?

[martinyonatann]

done. please help to review again @dmathieu @akats7