Rebrand file configuration to declarative configuration in documentation

[jack-berg]

Reflects the naming of this project in the spec: https://opentelemetry.io/docs/specs/otel/configuration/#declarative-configuration

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.37%. Comparing base (628db61) to head (4c0381b).
Report is 2 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #6812      +/-   ##
============================================
- Coverage     90.37%   90.37%   -0.01%     
  Complexity     6577     6577              
============================================
  Files           731      731              
  Lines         19714    19714              
  Branches       1926     1926              
============================================
- Hits          17817    17816       -1     
  Misses         1300     1300              
- Partials        597      598       +1     

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