refactor(otelhttp): change Version() func to const Version string

[dogedede]

Fixes #8134
Changes the Version() definition in the otelhttp package from a function to a constant string for simplicity and consistency.

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: dmathieu / name: Damien Mathieu (3a8e729, a5189d3, eb25c77)

[dogedede]

Apologies, I've updated the changelog.md.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 82.3%. Comparing base (2c083dd) to head (eb25c77).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #8142     +/-   ##
=======================================
- Coverage   82.3%   82.3%   -0.1%     
=======================================
  Files        195     194      -1     
  Lines      13800   13798      -2     
=======================================
- Hits       11359   11357      -2     
  Misses      2033    2033             
  Partials     408     408             

Files with missing lines	Coverage Δ
instrumentation/net/http/otelhttp/common.go	100.0% <100.0%> (ø)
instrumentation/net/http/otelhttp/config.go	83.0% <100.0%> (ø)

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