Support for gzip compression in OTLP exporter

[hannahhaering]

Implements #3961

Changes

• Added support for gzip compression to the OTLP exporter (HTTP and gRPC)
• Compression can be enabled via configuration/environment variables as per specification
• The first 5 bytes of gRPC messages have previously been created in the corresponding (Log, Trace, Metrics) exporter, centralized this in the ExportClient
• Added new tests for HTTP and gRPC export, with and without compression
• Extended the configuration tests to cover the new, compression related options

Validation/Testing

• Used the OpenTelemetry example Console application with compression enabled.
• Verified that traces were successfully exported to the OpenTelemetry Collector using both HTTP and gRPC, with gzip compression enabled.
• Confirmed that traces appeared correctly when routed through the collector.
• Verified that disabling compression continues to work as before.

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 (if applicable)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.83%. Comparing base (353bc85) to head (41dc747).
⚠️ Report is 43 commits behind head on main.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6494      +/-   ##
==========================================
+ Coverage   86.63%   86.83%   +0.20%     
==========================================
  Files         258      258              
  Lines       11878    11907      +29     
==========================================
+ Hits        10290    10340      +50     
+ Misses       1588     1567      -21     

Flag	Coverage Δ
unittests-Project-Experimental	86.46% <100.00%> (-0.09%)	⬇️
unittests-Project-Stable	86.77% <100.00%> (+0.25%)	⬆️

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

Files with missing lines	Coverage Δ
...ol/Implementation/ExportClient/OtlpExportClient.cs	100.00% <100.00%> (ø)
...mplementation/ExportClient/OtlpGrpcExportClient.cs	79.24% <100.00%> (+3.96%)	⬆️
...mplementation/ExportClient/OtlpHttpExportClient.cs	100.00% <100.00%> (ø)
...orter.OpenTelemetryProtocol/OtlpExporterOptions.cs	99.15% <100.00%> (+0.06%)	⬆️
....Exporter.OpenTelemetryProtocol/OtlpLogExporter.cs	88.00% <ø> (-1.66%)	⬇️
...porter.OpenTelemetryProtocol/OtlpMetricExporter.cs	77.27% <ø> (-3.50%)	⬇️
...xporter.OpenTelemetryProtocol/OtlpTraceExporter.cs	87.50% <ø> (-1.79%)	⬇️

... and 6 files with indirect coverage changes

[rajkumar-rangaraj]

@hannahhaering The OTLP Exporter currently lacks integration tests. With your proposed changes, did you test them with telemetry systems, and what were the results? Please update the PR description to include more details about how you tested with the collector or other services. It would be beneficial to verify with multiple sources.

[hannahhaering]

@hannahhaering The OTLP Exporter currently lacks integration tests. With your proposed changes, did you test them with telemetry systems, and what were the results? Please update the PR description to include more details about how you tested with the collector or other services. It would be beneficial to verify with multiple sources.

I updated the PR description.

[github-actions]

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[github-actions]

This PR was marked stale due to lack of activity and will be closed in 7 days. Commenting or pushing will instruct the bot to automatically remove the label. This bot runs once per day.