[OTLP] Respect configured options in UseOtlpExporter

[w3lld1]

Fixes #6231
Design discussion issue #6231

Changes

I updated UseOtlpExporter to resolve its default OtlpExporterOptions through the registered options pipeline instead of constructing a separate instance. This makes services.Configure<OtlpExporterOptions>(...) apply to the cross-cutting exporter while preserving signal-specific configuration and fallback behavior.

I also added a regression test that builds all three providers and verifies the configured endpoint reaches logging, metrics, and tracing.

Testing

• dotnet test test/OpenTelemetry.Exporter.OpenTelemetryProtocol.Tests/OpenTelemetry.Exporter.OpenTelemetryProtocol.Tests.csproj --framework net10.0 --no-restore (698 passed, 3 integration tests skipped)
• dotnet format test/OpenTelemetry.Exporter.OpenTelemetryProtocol.Tests/OpenTelemetry.Exporter.OpenTelemetryProtocol.Tests.csproj --no-restore --verify-no-changes
• python3 ./build/scripts/sanitycheck.py
• git diff --check origin/main...HEAD

The full solution matrix, including Windows/.NET Framework targets, is left to CI.

Merge requirement checklist

• CONTRIBUTING guidelines followed (license requirements, nullable enabled, static analysis, etc.)
• Unit tests added/updated
• Appropriate CHANGELOG.md files updated for non-trivial changes
• Changes in public API reviewed (not applicable; no public API change)

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: w3lld1 / name: w3lld1 (1c39f24, a0121a3)

[github-actions]

Welcome, contributor! Thank you for your contribution to opentelemetry-dotnet.

Important reminders:

• Read our Contributing Guidelines.
• Sign the CLA if you haven't already.
• Follow the OpenTelemetry Generative AI policy: disclose any AI use in your contribution, and communicate (PR descriptions, review replies) in your own words rather than AI-generated text.
• Give reviewers at least a few days before pinging them for feedback.
• If you need help with general setup, development process, or contributor etiquette, ask in #opentelemetry-new-contributors.

[opentelemetry-pr-dashboard]

Pull request dashboard status

• Status: Merged.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.21%. Comparing base (687b41b) to head (a0121a3).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7540      +/-   ##
==========================================
- Coverage   90.22%   90.21%   -0.02%     
==========================================
  Files         290      290              
  Lines       15967    15969       +2     
==========================================
  Hits        14406    14406              
- Misses       1561     1563       +2     

Flag	Coverage Δ
unittests-Project-Experimental	90.26% <100.00%> (-0.02%)	⬇️
unittests-Project-Stable	90.16% <100.00%> (-0.16%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
...enTelemetryProtocol/Builder/OtlpExporterBuilder.cs	100.00% <100.00%> (ø)
...etryProtocol/Builder/OtlpExporterBuilderOptions.cs	100.00% <100.00%> (ø)

... and 2 files with indirect coverage changes

[otelbot]

Thank you for your contribution @w3lld1! 🎉 We would like to hear from you about your experience contributing to OpenTelemetry by taking a few minutes to fill out this survey.