Ingestion control sampling rate note

[yuandesu]

What does this PR do? What is the motivation?

Adds a note to the Ingestion Controls doc stating that on short timeframes (e.g. 1h or 4h), the Effective Sampling Rate may show below 100% even when set to 100% because total traces are estimated—and that this does not mean traces are missing or the actual rate is below 100%.

Per APMS-18460 and Slack: the rate is computed from an estimated total trace count (we can’t get an exact count from how trace data is stored). That estimation can make the displayed value slightly under 100% on short timeframes. This PR documents that so customers know it’s expected and not missing data.

Merge instructions

Merge readiness:

• Ready for merge

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Additional notes

[github-actions]

Preview links (active after the build_preview check completes)

Modified Files

• https://docs-staging.datadoghq.com/yuandesu/ingestion-control-sampling-rate-note/tracing/trace_pipeline/ingestion_controls

[rtrieu]

hi yuan, thanks for the PR! made a suggestion that uses the active voice and simplifies the statements a bit. please request re-review when ready and i'll see it automatically.

[rtrieu]

Suggested change

	**Note**: On short time frames (such as 1 hour or 4 hours), the Effective Sampling Rate may display below `100%` even when set to `100%`, because the calculation estimates total traces. This does not mean traces are missing or that the actual rate is below 100%.