[cmd/mdatagen] [chore] Small fixes for new resource attributes filter

[dmitryax]

• Make sure we always pass a string to the filter.Match even if the attribute value has a different type. Otherwise, it panics.
• Make sure we show the if_configured warning if the user sets include/exclude without enabled.
• Simplify generated tests

Follow up to #9660

[codecov]

Codecov Report

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

Project coverage is 91.80%. Comparing base (878bba2) to head (335973e).

Files	Patch %	Lines
...plereceiver/internal/metadata/generated_metrics.go	71.42%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #9950      +/-   ##
==========================================
+ Coverage   91.75%   91.80%   +0.04%     
==========================================
  Files         358      358              
  Lines       16569    16568       -1     
==========================================
+ Hits        15203    15210       +7     
+ Misses       1038     1034       -4     
+ Partials      328      324       -4     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[dmitryax]

The coverage hasn't changed. I just touched a part that is not covered and probably don't need to be