feat(otel): copy service labels into GCM Metric

[dbolduc]

Fixes #14823

Credit to @IcySteam for raising the issue, and offering a fix for it in #14825. I also stole their tests. 😄

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Copy several well-known service labels from the resource into the metric, if they exist.

This avoids duplicate timeseries when multiple instances of a service are running on a single monitored resource, for example running multiple service processes on a single GCE VM.

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This change is 

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 92.91%. Comparing base (cb71d54) to head (0e0eac5).
Report is 5 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #14930   +/-   ##
=======================================
  Coverage   92.91%   92.91%           
=======================================
  Files        2351     2351           
  Lines      209811   209811           
=======================================
+ Hits       194948   194952    +4     
+ Misses      14863    14859    -4     

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