[CONFIGURATION] File configuration - spec stability

[marcalff]

Fixes # (issue)

Changes

Please provide a brief description of the changes here.

• Rename OTEL_EXPERIMENTAL_CONFIG_FILE to OTEL_CONFIG_FILE.

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

[marcalff]

Do not merge, blocked by:

• Mark declarative config as stable opentelemetry-specification#4568

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.98%. Comparing base (9cab071) to head (720c695).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3862      +/-   ##
==========================================
- Coverage   89.99%   89.98%   -0.01%     
==========================================
  Files         225      225              
  Lines        7170     7170              
==========================================
- Hits         6452     6451       -1     
- Misses        718      719       +1     

see 1 file with indirect coverage changes

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