[ML-OB] document metadata for custom evals

[lievan]

What does this PR do? What is the motivation?

This PR documents how to set the metadata field for evaluation metrics in the SDK

Merge instructions

• [ ] Please merge after reviewing

Additional notes

[github-actions[bot]]

Preview links (active after the build_preview check completes)

New or renamed files

• https://docs-staging.datadoghq.com/evan.li/metadata-for-evals-sdk/llm_observability/setup/sdk/

[maycmlee]

@lievan is this good to merge?

[lievan]

@maycmlee not yet; waiting on the next release of ddtrace, thanks!

[maycmlee]

@lievan Thanks for letting me know! Feel free to /merge when the next ddtrace has been released.

[lievan]

Holding off on supporting metadata for custom evals

[github-actions[bot]]

✅ Documentation Team Review

The documentation team has approved this pull request. Thank you for your contribution!

[lievan]

nevermind just gonna open a new one