Switch version from function to string in otelhttptrace

[eddyariki]

Change Version() func to const Version string in otelhttptrace

Part of #8272

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 82.3%. Comparing base (324aed7) to head (34d120d).

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #8383     +/-   ##
=======================================
- Coverage   82.3%   82.3%   -0.1%     
=======================================
  Files        183     182      -1     
  Lines      13766   13764      -2     
=======================================
- Hits       11331   11329      -2     
  Misses      2030    2030             
  Partials     405     405             

Files with missing lines	Coverage Δ
...on/net/http/httptrace/otelhttptrace/clienttrace.go	83.7% <100.0%> (ø)

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[dmathieu]

Duplicate of #8302