build(telemetry): update otelconf dependency to v0.19

[aaronc]

Description

Updates the https://pkg.go.dev/go.opentelemetry.io/contrib/otelconf dependency in telemetry/ to v0.19 which corresponds to a v1.0 RC of the OpenTelemetry declarative configuration format. This allows us to remove custom file exporters which we were using for testing because they are now supported upstream. It also requires some slight changes to the actual config format which are reflected in the README example configuration.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 70.29%. Comparing base (4818bc2) to head (1330bb8).
⚠️ Report is 3 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #25719      +/-   ##
==========================================
+ Coverage   68.28%   70.29%   +2.01%     
==========================================
  Files         870      835      -35     
  Lines       56500    54359    -2141     
==========================================
- Hits        38580    38212     -368     
+ Misses      17920    16147    -1773     

Files with missing lines	Coverage Δ
telemetry/config.go	2.46% <ø> (+0.98%)	⬆️

... and 38 files with indirect coverage changes

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