Document metrics grid aggregations in Discover

[miguel-sanchez-elastic]

Summary

• Document changing the default aggregation per metric type on the Metrics in Discover page.
• Relates to [Discover] Document metrics grid aggregations #8202. Blocked on [Metrics][Discover] Enable grid settings for all users kibana#288597 (not enabled for all users yet).
• After Document metrics grid sorting in Discover #8201 merges, this section should sit after Sort.

Test plan

• Check the docs preview for the aggregations subsection
• Confirm inline applies_to badges (Serverless, Stack 9.6+ / Planned)

Generative AI disclosure

1. Did you use a generative AI (GenAI) tool to assist in creating this contribution?

• Yes
• No

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🔍 Preview links for changed docs

• solutions/observability/infra-and-hosts/discover-metrics.md

[github-actions]

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[kpatticha]

lgtm

[mdbirnstiehl]

One comment, but otherwise LGTM.

[miguel-sanchez-elastic]

One comment, but otherwise LGTM.

Hi @mdbirnstiehl , I have applied the suggested change.

Let me know if the screenshot shows it in the way you expect it:

[mdbirnstiehl]

One comment, but otherwise LGTM.

Hi @mdbirnstiehl , I have applied the suggested change.

Let me know if the screenshot shows it in the way you expect it:

LGTM!

[miguel-sanchez-elastic]

Thank you @mdbirnstiehl !

We'll merge it once we deploy our changes on elastic/kibana#288597