[cmd/telemetrygen] Export telemetrygen functions for testing

[Erog38]

Description

This PR addresses #36984 in order to open up telemetrygen to be used by golang tests and generate varying amounts of telemetry in code to support use cases which don't rely on external tools.

Testing

Added to the E2E tests to ensure consistent API specs. Additionally had to adjust log and metric exporter instantiation slightly due to a race condition with an err variable.

[Erog38]

This goes hand in hand with #37003 in order to help own and maintain this API. I read about chloggen, but haven't used it before so I copied the template and made a version manually. I hope I did that properly.

[codecov]

Codecov Report

Attention: Patch coverage is 15.17857% with 190 lines in your changes missing coverage. Please review.

Project coverage is 79.57%. Comparing base (1629eda) to head (a719b82).
Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
cmd/telemetrygen/pkg/logs/logs.go	8.88%	39 Missing and 2 partials ⚠️
cmd/telemetrygen/pkg/metrics/metrics.go	8.88%	39 Missing and 2 partials ⚠️
cmd/telemetrygen/internal/common/config.go	0.00%	29 Missing ⚠️
cmd/telemetrygen/pkg/traces/config.go	15.15%	28 Missing ⚠️
cmd/telemetrygen/pkg/logs/config.go	35.13%	24 Missing ⚠️
cmd/telemetrygen/pkg/metrics/config.go	0.00%	18 Missing ⚠️
cmd/telemetrygen/pkg/metrics/metrics_types.go	0.00%	5 Missing ⚠️
cmd/telemetrygen/pkg/traces/traces.go	33.33%	2 Missing ⚠️
cmd/telemetrygen/config.go	75.00%	1 Missing ⚠️
cmd/telemetrygen/pkg/metrics/worker.go	75.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #37044      +/-   ##
==========================================
- Coverage   79.60%   79.57%   -0.03%     
==========================================
  Files        2250     2250              
  Lines      211890   211951      +61     
==========================================
- Hits       168676   168668       -8     
- Misses      37540    37608      +68     
- Partials     5674     5675       +1     

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