Add declarative support for composable parent threshold sampler

[jack-berg]

https://github.com/open-telemetry/opentelemetry-configuration/blob/main/schema-docs.md#experimentalcomposableparentthresholdsampler-

[codecov]

Codecov Report

❌ Patch coverage is 83.33333% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 90.13%. Comparing base (a988380) to head (01686cb).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
...incubator/fileconfig/ComposableSamplerFactory.java	83.33%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff            @@
##               main    #7941   +/-   ##
=========================================
  Coverage     90.13%   90.13%           
- Complexity     7442     7467   +25     
=========================================
  Files           834      834           
  Lines         22549    22586   +37     
  Branches       2237     2240    +3     
=========================================
+ Hits          20324    20358   +34     
- Misses         1528     1529    +1     
- Partials        697      699    +2     

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[jkwatson]

Thanks!