[cmd/mdatagen] Pull new changes from contrib

[dmitryax]

To completely migrate mdatagen from contrib to core, we need to pull latest changes:

• [chore] [mdatagen] Use directory name as package name for generated files opentelemetry-collector-contrib#31500
• [chore] [cmd/mdatagen] Move sample-metadata.yaml to a separate package opentelemetry-collector-contrib#31503
• [chore] [cmd/mdatagen] Remove dependency on an internal package opentelemetry-collector-contrib#31520
• [chore][cmd/mdatagen] remove unused generated code opentelemetry-collector-contrib#31525
• [chore] [cmd/mdatagen] Use enum for stability levels opentelemetry-collector-contrib#31530
• [cmd/mdatagen] Make lifecycle tests generated by default opentelemetry-collector-contrib#31532

[codecov]

Codecov Report

Attention: Patch coverage is 75.00000% with 12 lines in your changes are missing coverage. Please review.

Project coverage is 90.93%. Comparing base (e696206) to head (6ad0691).

Files	Patch %	Lines
cmd/mdatagen/statusdata.go	62.50%	8 Missing and 1 partial ⚠️
cmd/mdatagen/main.go	50.00%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #9683      +/-   ##
==========================================
- Coverage   90.93%   90.93%   -0.01%     
==========================================
  Files         347      348       +1     
  Lines       18346    18379      +33     
==========================================
+ Hits        16683    16713      +30     
- Misses       1340     1344       +4     
+ Partials      323      322       -1     

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[dmitryax]

@codeboten, thank you for creating all the issues!