feat(instrumentation/http/otelhttp): move client metrics creation into internal semconv package

[VinozzZ]

In preparation for implementing OTEL_SEMCONV_STABILITY_OPT_IN for HTTP client metrics, this is the first PR to emit only old client metrics. This PR will enable us to add the ability for otelhttp to emit both old and new client metrics.

Address issue #5973

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 67.2%. Comparing base (900fc4b) to head (cc38490).
Report is 1 commits behind head on main.

Additional details and impacted files

@@          Coverage Diff          @@
##            main   #6002   +/-   ##
=====================================
  Coverage   67.1%   67.2%           
=====================================
  Files        194     194           
  Lines      12709   12766   +57     
=====================================
+ Hits        8533    8584   +51     
- Misses      3901    3904    +3     
- Partials     275     278    +3     

Files with missing lines	Coverage Δ
instrumentation/net/http/otelhttp/common.go	100.0% <ø> (ø)
instrumentation/net/http/otelhttp/handler.go	91.9% <100.0%> (+1.8%)	⬆️
...entation/net/http/otelhttp/internal/semconv/env.go	92.0% <100.0%> (+3.3%)	⬆️
...tion/net/http/otelhttp/internal/semconv/v1.20.0.go	94.4% <100.0%> (+3.2%)	⬆️
instrumentation/net/http/otelhttp/transport.go	94.3% <100.0%> (-0.9%)	⬇️

... and 2 files with indirect coverage changes

[MrAlias]

It looks like the lint CI is failing. Please run make precommit, it should fix the issue.

[dashpole]

This is now ready for review.

[XSAM]

@open-telemetry/go-approvers PTAL

[XSAM]

Overall, it looks good to me. I only have this question to address. #6002 (comment)