refactor(otelgin): switch version from function to string

[ElenaZvereva]

Change Version() func to const Version string in otelgin
Part of #8272

[codecov]

Codecov Report

❌ Patch coverage is 66.66667% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 82.3%. Comparing base (6e187c4) to head (2f875e9).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
...umentation/github.com/gin-gonic/gin/otelgin/gin.go	66.6%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #8341     +/-   ##
=======================================
- Coverage   82.3%   82.3%   -0.1%     
=======================================
  Files        182     181      -1     
  Lines      13764   13762      -2     
=======================================
- Hits       11329   11327      -2     
  Misses      2030    2030             
  Partials     405     405             

Files with missing lines	Coverage Δ
...umentation/github.com/gin-gonic/gin/otelgin/gin.go	92.9% <66.6%> (ø)

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Requested changes have been applied.