refactor: move example from otelgin to make it a testable example

[mcapell]

Following this PR, this moves the example from otelgin to be displayed in godocs.

Resolves: #7063

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: mcapell / name: Marc Capell (3d6f8b3)
• ✅ login: pellared / name: Robert Pająk (6267aeb, 639fb9f, 92377a1, 0a1ffab)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 81.4%. Comparing base (878b3a7) to head (92377a1).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #7328     +/-   ##
=======================================
+ Coverage   81.2%   81.4%   +0.2%     
=======================================
  Files        207     206      -1     
  Lines      18275   18230     -45     
=======================================
  Hits       14845   14845             
+ Misses      3008    2963     -45     
  Partials     422     422             

see 3 files with indirect coverage changes

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[flc1125]

Thank you for your contribution.

I don't think we need to remove the examples. What I believe we should do is: simply add examples based on the pkg.go.dev documentation (similar to the example_test.go format).

Just wanted to confirm, is this what we need? @pellared

[flc1125]

PS: To facilitate testing whether the desired effect is achieved, you can use this tool for debugging: https://github.com/golang/pkgsite

[pellared]

This also follows: #7118