Consistent application of exporter customizers when otel.{signal}.exporter=none

[jack-berg]

While working on something else, I noticed a discrepancy between how autoconfigure handles exporter customization via SPI when otel.metrics.exporter=none, compared to otel.traces.exporter=none and otel.logs.exporter=none.

For traces and logs, when exporter is set to none, we still invoke any respective exporter customizers registered via AutoConfigurationCustomizer#addSpanExporterCustomizer, AutoConfigurationCustomizer#addLogRecordExporterCustomizer. For metrics, we do not apply such a AutoConfigurationCustomizer#addMetricExporterCustomizer when exporter is set to none.

This PR standardizes on the the metrics approach of not applying exporter customizers when exporter is set to none.

While you can make arguments for either approach, the metrics approach is more correct / defensible since its less surprising. I don't think many people would intuit that exporter customizers have a chance to intervene when the user intends to set the exporter to none.

[jack-berg]

This was interfering with the changes I was making to FullConfigTest. Setting span limits is well tested elsewhere, and we should limit the integration-style FullConfigTest to concepts that really require everything to be stood up in an end-to-end fashion.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.98%. Comparing base (4b3cedd) to head (6dfbb06).
Report is 5 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #7017      +/-   ##
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+ Coverage     89.95%   89.98%   +0.02%     
+ Complexity     6636     6635       -1     
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  Files           745      745              
  Lines         20010    20000      -10     
  Branches       1962     1960       -2     
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- Hits          18000    17996       -4     
+ Misses         1415     1408       -7     
- Partials        595      596       +1     

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[breedx-splk]

Thanks for noticing and fixing the inconsistency! It would definitely be surprising to someone somewhere if they specified otel.{signal}.exporter=none and some customizer injected an exporter anyway. And I agree with your assessment that you could argue for/against this approach, but I think this way is the most practical/sensical.