[otelcol] Add featuregate to use stable expansion rules

[TylerHelmuth]

Description

This PR adds a feature gate to control all our use of the expandconverter. When enabled, the feature gate will use DefaultScheme="env" instead of the expandconverter for OCB and when supplying default providers in NewCommand.

Alternative to #10259

Link to tracking issue

Related to #10161
Related to #8215
Related to #7111

Testing

Unit tests

[codecov]

Codecov Report

Attention: Patch coverage is 50.00000% with 3 lines in your changes missing coverage. Please review.

Project coverage is 92.53%. Comparing base (a6ace53) to head (ce20c63).

Files	Patch %	Lines
otelcol/configprovider.go	50.00%	1 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #10361      +/-   ##
==========================================
- Coverage   92.54%   92.53%   -0.02%     
==========================================
  Files         387      387              
  Lines       18254    18258       +4     
==========================================
+ Hits        16894    16895       +1     
- Misses       1015     1016       +1     
- Partials      345      347       +2     

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