[CI] build examples with IWYU

[marcalff]

Fixes # (issue)

Changes

Please provide a brief description of the changes here.

• Expand the iwyu CI to cover examples
• Fixed the issues reported

For significant contributions please make sure you have completed the following items:

• CHANGELOG.md updated for non-trivial changes
• Unit tests have been added
• Changes in public API reviewed

[netlify]

✅ Deploy Preview for opentelemetry-cpp-api-docs canceled.

Name	Link
🔨 Latest commit	10b26fa
🔍 Latest deploy log	https://app.netlify.com/projects/opentelemetry-cpp-api-docs/deploys/683a0389341c1b000875c7a4

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.88%. Comparing base (7a847ca) to head (10b26fa).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3450      +/-   ##
==========================================
+ Coverage   89.86%   89.88%   +0.02%     
==========================================
  Files         212      212              
  Lines        6941     6941              
==========================================
+ Hits         6237     6238       +1     
+ Misses        704      703       -1     

see 1 file with indirect coverage changes

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[dbarker]

The iwyu tool never makes it to the otlp grpc examples due to a segfault (#3453). This isn't new so shouldn't block this PR.