Templateize the request http package

[dmathieu]

This package is used by both otelhttp and otelmux, and should be used by all packages using the semconv HTTP package.
So this templateizes is to make its reuse easier.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 73.8%. Comparing base (30c5607) to head (c8f6ccd).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #6709     +/-   ##
=======================================
- Coverage   73.9%   73.8%   -0.1%     
=======================================
  Files        195     195             
  Lines      16627   16627             
=======================================
- Hits       12291   12282      -9     
- Misses      3978    3984      +6     
- Partials     358     361      +3     

Files with missing lines	Coverage Δ
...rilla/mux/otelmux/internal/request/body_wrapper.go	93.7% <ø> (ø)
...ux/otelmux/internal/request/resp_writer_wrapper.go	94.5% <ø> (-5.5%)	⬇️
...net/http/otelhttp/internal/request/body_wrapper.go	100.0% <ø> (ø)
...p/otelhttp/internal/request/resp_writer_wrapper.go	100.0% <ø> (ø)

... and 1 file with indirect coverage changes