DOCS-3873 add examples for manual keep and drop

[kayayarai]

What does this PR do?

Expands on the examples given for manually keeping or dropping spans on ingestion

Motivation

DOCS3873

Additional Notes

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Reviewer checklist

• [ ] Review the changed files.
• [ ] Review the URLs listed in the Preview section.
• [ ] Check images for PII
• [ ] Review any mentions of "Contact Datadog support" for internal support documentation.

[github-actions[bot]]

Preview links (active after the build_preview check completes)

Modified Files

• https://docs-staging.datadoghq.com/kari/docs-3873-keep-drop/tracing/trace_pipeline/ingestion_mechanisms

[kayayarai]

This branch got too old. Reopened as https://github.com/DataDog/documentation/pull/16089