mdatagen: get package name from metadata

[braydonk]

Description

I noticed a mistake in my previous PR #11232; some function calls did not pass the correct package name in (passing in "metadata" instead of the intended generated package name). This PR attempts to address the potential for this mistake to even occur by providing a wrapper generateFile function that automatically uses the generated package name from the metadata. The original version of the function that accepts a package name is intact for the templates that are going in the base package instead of the generated one.

Link to tracking issue

Bug originally from #11231
Fixes #11469

Testing

make mdatagen-test

Also added a custom generated package to the sample components, which would have caught the original bug.

Documentation

[braydonk]

I believe this change should not need a changelog. It is a fix for a bug that never made it into a release, and otherwise provides no user-visible changes.

[codecov]

Codecov Report

Attention: Patch coverage is 87.78195% with 65 lines in your changes missing coverage. Please review.

Project coverage is 92.04%. Comparing base (388bae7) to head (a7da76a).

Files with missing lines	Patch %	Lines
...amplereceiver/internal/custom/generated_metrics.go	91.69%	23 Missing and 2 partials ⚠️
...plereceiver/internal/custom/generated_telemetry.go	65.45%	19 Missing ⚠️
...samplereceiver/internal/custom/generated_config.go	87.30%	4 Missing and 4 partials ⚠️
...ampleprocessor/internal/custom/generated_config.go	88.23%	2 Missing and 2 partials ⚠️
cmd/mdatagen/internal/command.go	66.66%	0 Missing and 3 partials ⚠️
...pleprocessor/internal/custom/generated_resource.go	91.42%	3 Missing ⚠️
...mplereceiver/internal/custom/generated_resource.go	91.42%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #11468      +/-   ##
==========================================
- Coverage   92.14%   92.04%   -0.10%     
==========================================
  Files         433      439       +6     
  Lines       20389    20914     +525     
==========================================
+ Hits        18787    19250     +463     
- Misses       1238     1292      +54     
- Partials      364      372       +8     

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[braydonk]

The new coverage issue are just for the generated custom package I added, which I don't think are any more/less covered than the other generated metadata package and are just there as goldens anyway. So I think the codecov can be accepted.