Upgrade OTLP to 1.8.0

[dmathieu]

This PR upgrades OTLP to 1.8.0.
See https://github.com/open-telemetry/opentelemetry-proto/releases/tag/v1.8.0

-contrib counterpart coming soon (I will move this out of draft once both PRs are ready).

[codecov]

Codecov Report

❌ Patch coverage is 93.21267% with 45 lines in your changes missing coverage. Please review.
✅ Project coverage is 91.39%. Comparing base (8c24052) to head (47313be).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
pdata/internal/generated_wrapper_stack.go	84.67%	15 Missing and 4 partials ⚠️
...data/internal/generated_wrapper_keyvalueandunit.go	93.95%	6 Missing and 3 partials ⚠️
pdata/pprofile/generated_keyvalueandunitslice.go	89.85%	5 Missing and 2 partials ⚠️
pdata/pprofile/attributes.go	66.66%	4 Missing and 2 partials ⚠️
pdata/internal/generated_wrapper_sample.go	92.98%	4 Missing ⚠️

❌ Your patch status has failed because the patch coverage (93.21%) is below the target coverage (95.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #13758      +/-   ##
==========================================
- Coverage   91.44%   91.39%   -0.06%     
==========================================
  Files         640      644       +4     
  Lines       42665    42553     -112     
==========================================
- Hits        39016    38890     -126     
- Misses       2831     2841      +10     
- Partials      818      822       +4     

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[florianl]

I focused on pprofiles and its related changes.