[chore] service: refactor otelconftelemetry-related code

[axw]

Description

Refactor some code so we can reduce the dependency tree (in a followup).

Replace TestServiceTelemetryConsistentInstanceID in the service package with a functional test under internal/e2e. The new test verifies telemetry by running the collector and sending a request to the otlp receiver, and then checking the resulting internal telemetry is as expected. The purpose of this change is to test behaviour, rather than implementation, to simplify further refactoring.

Move service/telemetry/internal/migration to service/telemetry/otelconftelemetry/internal/migration, since it's only used by otelconftelemetry.

Link to tracking issue

Part of #13809

Testing

N/A

Documentation

N/A

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.79%. Comparing base (5e41fb5) to head (a74fd59).

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #14308      +/-   ##
==========================================
- Coverage   91.80%   91.79%   -0.01%     
==========================================
  Files         677      677              
  Lines       42536    42536              
==========================================
- Hits        39050    39047       -3     
- Misses       2425     2427       +2     
- Partials     1061     1062       +1     

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[codspeed-hq]

CodSpeed Performance Report

Merging this PR will not alter performance

_{Comparing axw:service-move-otelconftelemetry-uses (a74fd59) with main (5e41fb5)}

⚠️ Unknown Walltime execution environment detected

Using the Walltime instrument on standard Hosted Runners will lead to inconsistent data.

For the most accurate results, we recommend using CodSpeed Macro Runners: bare-metal machines fine-tuned for performance measurement consistency.

Summary

✅ 61 untouched benchmarks
⏩ 20 skipped benchmarks¹

Footnotes

1. 20 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩