Support OTLP standard environment variables for configuration

[damienpontifex]

Support open telemetry standard environment variables for OTLP exporter

Systems often inject these variables, or equally developers expect to have a consistent set of configuration options when relating to opentelemetry. Environment variables for the open telemetry OTLP exporter are outlined at https://opentelemetry.io/docs/languages/sdk-configuration/otlp-exporter/ for their standards.

This adds in the option to utilise those environment variables, without introducing a breaking change, by falling back to the currently documented process.

Relevant issues

Relates to #9901

Also relates to PR #9972 but I had confusion on that PR, as it doesn't reference environment variables such as OTEL_EXPORTER_OTLP_PROTOCOL, or OTEL_EXPORTER_OTLP_ENDPOINT as I had expected

Pre-Submission checklist

Please complete all items before asking a LiteLLM maintainer to review your PR

• [ ] I have Added testing in the tests/litellm/ directory, Adding at least 1 test is a hard requirement - see details
• [ ] I have added a screenshot of my new test passing locally
• [ ] My PR passes all unit tests on make test-unit
• [x] My PR's scope is as isolated as possible, it only solves 1 specific problem

Type

🆕 New Feature 📖 Documentation

Changes

• Default to OTLP standard, but fallback to existing so as to not break backwards compatibility
• Also allow/match the values expected in OTEL_EXPORTER_OTLP_PROTOCOL of grpc, http/protobuf, or http/json as outlined at https://opentelemetry.io/docs/languages/sdk-configuration/otlp-exporter/#otel_exporter_otlp_protocol
• Changed documentation on the "Log to OTEL HTTP Collector" and "Log to OTEL GRPC Collector" tabs as they seem more related to OTLP standards than the other documented tabs

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Name	Status	Preview	Comments	Updated (UTC)
litellm	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	May 14, 2025 1:58am

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[damienpontifex]

Apologies for not running tests locally, had all sorts of errors on "Installing tiktoken" that I'd have to dive into much deeper than an environment variable change to understand