[CONFIGURATION] File configuration - functional tests

[marcalff]

Contributes to #2481

This is a partial fix, to implement functional tests for file configuration.

Changes

Please provide a brief description of the changes here.

• Implement functional tests for file configuration.
• Fix missing include in string_util.h, for isspace.
• Code cleanup in sdk_builder.cc, now that issue [SDK] View should not have a unit #3547 is resolved.

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]

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.02%. Comparing base (6d7b8ad) to head (fc5f0c7).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3606      +/-   ##
==========================================
- Coverage   90.03%   90.02%   -0.01%     
==========================================
  Files         220      220              
  Lines        7069     7069              
==========================================
- Hits         6364     6363       -1     
- Misses        705      706       +1     

Files with missing lines	Coverage Δ
api/include/opentelemetry/common/string_util.h	100.00% <ø> (ø)

... and 1 file with indirect coverage changes

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[dbarker]

Looks good. Thanks!