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]

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• ✅ login: dogedede / name: Andy (448ae1e)

[dogedede]

Apologies, I've updated the changelog.md.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.8%. Comparing base (7ff03d6) to head (37c0b45).

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #8142     +/-   ##
=======================================
- Coverage   81.8%   81.8%   -0.1%     
=======================================
  Files        194     193      -1     
  Lines      13362   13360      -2     
=======================================
- Hits       10936   10934      -2     
  Misses      2029    2029             
  Partials     397     397             

Files with missing lines	Coverage Δ
instrumentation/net/http/otelhttp/common.go	100.0% <100.0%> (ø)
instrumentation/net/http/otelhttp/config.go	82.0% <100.0%> (ø)

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[dmathieu]

@open-telemetry/go-approvers I think we could make it more visible this is a breaking change. But at the same time, doing something too prominent for the version string probably too much. WDYT?

[flc1125]

I prefer to only mark content or tags related to significant changes here.