optional internal metrics

[brettmc]

adding a configuration option OTEL_PHP_INTERNAL_METRICS_ENABLED which controls whether the SDK will emit its own metrics (eg batch processor state).

[codecov]

Codecov Report

Merging #1106 (9315c8f) into main (82f0c44) will decrease coverage by 0.09%.
Report is 1 commits behind head on main.
The diff coverage is 100.00%.

❗ Current head 9315c8f differs from pull request most recent head 3dd1079. Consider uploading reports for the commit 3dd1079 to get more accurate results

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #1106      +/-   ##
============================================
- Coverage     83.13%   83.05%   -0.09%     
+ Complexity     2202     2151      -51     
============================================
  Files           282      278       -4     
  Lines          6275     6119     -156     
============================================
- Hits           5217     5082     -135     
+ Misses         1058     1037      -21     

Flag	Coverage Δ
7.4	81.66% <100.00%> (-0.12%)	⬇️
8.0	82.97% <100.00%> (-0.09%)	⬇️
8.1	83.11% <100.00%> (-0.09%)	⬇️
8.2	83.11% <100.00%> (-0.09%)	⬇️

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Files Changed	Coverage Δ
src/SDK/Common/Time/SystemClock.php	64.28% <ø> (+19.28%)	⬆️
src/SDK/Metrics/MeterProviderBuilder.php	0.00% <ø> (ø)
src/SDK/Resource/ResourceInfoFactory.php	100.00% <ø> (+11.36%)	⬆️
src/SDK/SdkAutoloader.php	93.93% <100.00%> (+0.18%)	⬆️

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