mdatagen: support custom package name

[braydonk]

Description

This PR adds support for a new --package_name flag generated_package_name config field to allow mdatagen to generate packages with names other than metadata.

Link to tracking issue

Fixes #11231

Testing

• Unit tests
• go installing this branch and using it in a test scenario with two yaml files and generating two packages.

Documentation

[codeboten]

Overall this looks pretty good, just a couple of comments, it looks like make gofmt needs to be run to sort out the import statements. Also please add a note in the schema file: https://github.com/open-telemetry/opentelemetry-collector/blob/main/cmd/mdatagen/metadata-schema.yaml

[braydonk]

Also please add a note in the schema file

Done in d6c50bf

I believe running make gofmt in 554391b addressed all other comments.

[codecov]

Codecov Report

Attention: Patch coverage is 71.42857% with 2 lines in your changes missing coverage. Please review.

Project coverage is 92.15%. Comparing base (68f0264) to head (b142b2b).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
cmd/mdatagen/internal/command.go	60.00%	0 Missing and 2 partials ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #11232   +/-   ##
=======================================
  Coverage   92.15%   92.15%           
=======================================
  Files         432      432           
  Lines       20291    20293    +2     
=======================================
+ Hits        18700    18702    +2     
  Misses       1228     1228           
  Partials      363      363           

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[codeboten]

Thanks for the update @braydonk, looks good now, can merge it once the conflict has been resolved