[Code health] Include what you use cleanup, part 5

[marcalff]

Contributes to #2054

Changes

Please provide a brief description of the changes here.

• continued the include-what-you-use cleanup
• total number of warnings decreased from 37 in branch main, to 2 in this PR.
• CI is now enforcing a pass/fail check, with some tolerance (<= 10 warnings)

Note that the cleanup is not completed, as some optional parts (OTLP GRPC) are not covered yet by the build in CI.
This will be handled in subsequent PRs.

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

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 87.86%. Comparing base (8d45dec) to head (04082ca).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3140   +/-   ##
=======================================
  Coverage   87.86%   87.86%           
=======================================
  Files         195      195           
  Lines        6151     6151           
=======================================
  Hits         5404     5404           
  Misses        747      747           

Files with missing lines	Coverage Δ
api/include/opentelemetry/nostd/variant.h	66.67% <ø> (ø)
...telemetry/exporters/memory/in_memory_metric_data.h	100.00% <ø> (ø)
exporters/memory/src/in_memory_metric_data.cc	85.00% <ø> (ø)
...rs/memory/src/in_memory_metric_exporter_factory.cc	100.00% <ø> (ø)
...xporters/memory/test/in_memory_metric_data_test.cc	100.00% <ø> (ø)
...ters/memory/test/in_memory_metric_exporter_test.cc	100.00% <ø> (ø)
exporters/memory/test/in_memory_span_data_test.cc	100.00% <ø> (ø)
...orters/memory/test/in_memory_span_exporter_test.cc	100.00% <ø> (ø)
exporters/ostream/test/ostream_log_test.cc	96.18% <ø> (ø)
exporters/ostream/test/ostream_metric_test.cc	100.00% <ø> (ø)
... and 2 more

[marcalff]

@open-telemetry/cpp-contrib-approvers Ready for review.

[marcalff]

@ThomsonTan @lalitb @esigo @owent

Any chance to approve this cleanup, so it goes into release 1.18.0 ?

[marcalff]

@owent

Thanks for the review.
All comments fixed, PTAL.

[esigo]

LGTM
thanks for the PR :)

[owent]

LGTM and thanks.