[Security Assistant] Fixes LangSmith support for specifying configuration via env vars

[spong]

Summary

With #180227, LangSmith configuration (Project & API Key) could no longer be specified using environment variables when working locally. This fixes that issue, which was caused by sending '' for langSmithProject and langSmithApiKey instead of undefined.

To test, set the below env vars, then start kibana. Be sure to not have the UI trace options set as shown in #180227.

# LangChain LangSmith
export LANGCHAIN_TRACING_V2=true
export LANGCHAIN_ENDPOINT="https://api.smith.langchain.com"
export LANGCHAIN_API_KEY="🫣"
export LANGCHAIN_PROJECT="Best Project Ever"

[elasticmachine]

Pinging @elastic/security-solution (Team: SecuritySolution)

[spong]

It's fine to pass in undefined as the projectName here. LangChain will attempt to fetch it from the env vars, and if still not available it will then fall back to default when pushing to LangSmith.

[stephmilovic]

Thanks for getting this fixed quickly. Ran your test and had success, LGTM!

[kibana-ci]

💚 Build Succeeded

• Buildkite Build
• Commit: cb656f6

Metrics [docs]

Async chunks

Total size of all lazy-loaded chunks that will be downloaded as the user navigates the app

id	before	after	diff
securitySolution	17.0MB	17.0MB	+83.0B

To update your PR or re-run it, just comment with:
@elasticmachine merge upstream

cc @spong