Metrics Namespace Edit

[alai97]

What does this PR do? What is the motivation?

Customer support ticket which identified that the formula for calculating the average latency with host tag filters is not up-to-date.

Flagged by Yoshiya on #documentation Slack

Merge instructions

• [x] Please merge after reviewing

Additional notes

[github-actions[bot]]

Preview links (active after the build_preview check completes)

Modified Files

• https://docs-staging.datadoghq.com/alai97/tracing-metrics-namespace-edit/tracing/metrics/metrics_namespace