feat(otel): add OTLP/gRPC export support

[stoopman]

Summary

• Honour OTEL_EXPORTER_OTLP_PROTOCOL when configuring OTLP trace and log export
• Add opentelemetry-exporter-otlp-proto-grpc to the otel extra and select gRPC exporters when OTEL_EXPORTER_OTLP_PROTOCOL=grpc
• Resolve exporter endpoints per protocol (HTTP keeps /v1/traces and /v1/logs; gRPC uses the base collector URL)

Fixes Flagsmith/flagsmith#7812

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: ASSERTIVE

Plan: Pro Plus

Run ID: dc37c6f1-1640-44bd-88c8-c94bc2bbaf90

📥 Commits

Reviewing files that changed from the base of the PR and between 7bc5dcc and d778510.

📒 Files selected for processing (6)

• README.md
• src/common/core/constants.py
• src/common/core/main.py
• src/common/core/otel.py
• src/common/core/types.py
• tests/unit/common/core/test_otel.py

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📝 Walkthrough

Walkthrough

Adds OTLP gRPC transport support alongside the existing HTTP transport in OpenTelemetry setup. Endpoint resolution and provider construction now use the configured protocol, with ensure_cli_env passing protocol-specific endpoints to log and trace providers. The gRPC exporter dependency, unit tests, and README OpenTelemetry documentation are updated.

Estimated code review effort: 3 (Moderate) | ~25 minutes

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[khvn26]

Thanks for contributing to Flagsmith's OTel support @stoopman, very happy to see people using it!

The PR mostly LGTM, with a couple questions from my side.

Also, it seems there are typing errors to resolve still.

[stoopman]

@khvn26 Thanks for your review, I've pushed some updates which handle your requested changes

[khvn26]

LGTM with two nitpicks — feel free to address them if you like.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.58%. Comparing base (83e5d1a) to head (d778510).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #247      +/-   ##
==========================================
+ Coverage   97.56%   97.58%   +0.02%     
==========================================
  Files         108      109       +1     
  Lines        4757     4802      +45     
==========================================
+ Hits         4641     4686      +45     
  Misses        116      116              

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[stoopman]

LGTM with two nitpicks — feel free to address them if you like.

@khvn26 Thanks! I made some minor adjustments