Better explain STATS on multivalued fields

[nik9000]

Updates the docs for multivalued fields to make it clear that grouping puts the entire row in each group.

Relates to #134792

[elasticsearchmachine]

Pinging @elastic/es-analytical-engine (Team:Analytics)

[elasticsearchmachine]

Pinging @elastic/core-docs (Team:Docs)

[github-actions]

ℹ️ Important: Docs version tagging

👋 Thanks for updating the docs! Just a friendly reminder that our docs are now cumulative. This means all 9.x versions are documented on the same page and published off of the main branch, instead of creating separate pages for each minor version.

We use applies_to tags to mark version-specific features and changes.

Expand for a quick overview

When to use applies_to tags:

✅ At the page level to indicate which products/deployments the content applies to (mandatory)
✅ When features change state (e.g. preview, ga) in a specific version
✅ When availability differs across deployments and environments

What NOT to do:

❌ Don't remove or replace information that applies to an older version
❌ Don't add new information that applies to a specific version without an applies_to tag
❌ Don't forget that applies_to tags can be used at the page, section, and inline level

🤔 Need help?

• Check out the cumulative docs guidelines
• Reach out in the #docs Slack channel

[craigtaverner]

LGTM

[craigtaverner]

OK, so you are really emphasising this! Probably necessary, since it is far from obvious.

[leemthompo]

@craigtaverner @nik9000 looking at the preview for this page raised a question in my mind:

is there any reason we can't use actual headings in these command references? For biggish pages like this one, we have no On this page orientation, because we just use bold text instead of actual headings.

It would help us break up the walls of examples into scannable subgroups too, for example.

Not to be tackled in this PR, of course, but might be a UX improvement I/we can follow up on. :)

[nik9000]

I don't see a reason why we can't make more headings.

[elasticsearchmachine]

💚 Backport successful

Status	Branch	Result
✅	9.1
✅	9.0