Enable sensitive data for langchain programmatically

[rads-1996]

No description provided.

[github-actions]

Performance comparison

Threshold: regressions >15.0% on gating scenarios fail the build. Higher ops/s is better; positive Δ means the PR is slower.

Scenario	Gating	Baseline (ops/s)	Candidate (ops/s)	Δ %	Status
azure_monitor_log	yes	27,929.8	28,198.4	-0.95%	✅
azure_monitor_span	yes	158,730.2	161,550.9	-1.75%	✅
otel_log	no	32,769.7	33,184.0	-1.25%	✅
otel_span	no	43,715.8	44,120.9	-0.92%	✅

[Copilot]

Pull request overview

This PR adds programmatic support in use_microsoft_opentelemetry(...) for enabling LangChain/GenAI message content capture by wiring new kwargs (enable_experimental_mode, capture_message_content) to the upstream environment variables read by opentelemetry-util-genai and the in-repo LangChain helpers.

Changes:

• Add new public kwargs to use_microsoft_opentelemetry(...) that set OTEL_SEMCONV_STABILITY_OPT_IN and (when valid) OTEL_INSTRUMENTATION_GENAI_CAPTURE_MESSAGE_CONTENT.
• Introduce shared constants for the env var names and allowed capture modes.
• Add unit/integration tests and update the LangChain sample README to document the kwarg-based configuration.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
src/microsoft/opentelemetry/_distro.py	Implements kwarg → env-var wiring and warning behavior for invalid/ignored values.
src/microsoft/opentelemetry/_constants.py	Adds kwarg names, env var keys, and allowed capture-mode values.
tests/test_distro.py	Adds tests validating env-var propagation semantics and non-overwrite behavior.
tests/test_langchain_integration.py	Adds integration coverage verifying the wiring matches what LangChain content-capture utilities read.
samples/langchain/README.md	Documents using kwargs instead of exporting env vars, plus accepted values.

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[JacksonWeber]

LGTM