[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 87.83%. Comparing base (497eaf4) to head (6c70301).
Report is 164 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3140      +/-   ##
==========================================
+ Coverage   87.12%   87.83%   +0.72%     
==========================================
  Files         200      195       -5     
  Lines        6109     6146      +37     
==========================================
+ Hits         5322     5398      +76     
+ Misses        787      748      -39     

Files with missing lines	Coverage Δ
...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> (-0.04%)	⬇️
exporters/ostream/test/ostream_metric_test.cc	100.00% <ø> (ø)
exporters/ostream/test/ostream_span_test.cc	100.00% <ø> (ø)
... and 1 more

... and 106 files with indirect coverage changes

[marcalff]

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