[Metrics UI] Add warning severity to Metric Alerts

[Zacqary]

Summary

Closes #88591
Closes #89912
Should also fix #89807

Screenshots are from the Metric Threshold alert type, but the Warning threshold is also available on the Inventory alert type. Test them both during PR review.

Checklist

• Any text added follows EUI's writing guidelines, uses sentence case text and includes i18n support

• Unit or functional tests were updated or added to match the most common scenarios

• Any UI touched in this PR is usable by keyboard only (learn more about keyboard accessibility)

• Any UI touched in this PR does not create any new axe failures

• This renders correctly on smaller devices using a responsive layout. (You can test this in your browser)

[elasticmachine]

Pinging @elastic/logs-metrics-ui (Team:logs-metrics-ui)

[kibanamachine]

💚 Build Succeeded

• continuous-integration/kibana-ci/pull-request
• Commit: f5f4170

Metrics [docs]

Async chunks

Total size of all lazy-loaded chunks that will be downloaded as the user navigates the app

id	before	after	diff
infra	1.9MB	1.9MB	+16.9KB

Page load bundle

Size of the bundles that are downloaded on every page load. Target size is below 100kb

id	before	after	diff
infra	172.5KB	173.8KB	+1.4KB

History

• 💚 Build #103948 succeeded ea26c58
• 💔 Build #103930 failed e7ae38c
• 💔 Build #103622 failed e61d9ca
• 💔 Build #103511 failed 111b3d9
• 💔 Build #103131 failed fd824ee

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@elasticmachine merge upstream

[simianhacker]

I have 10 hosts reporting an average around 12-20%, then I have one host that is pushing 100% (which averages out to about 50% (ish). When I set the threshold to 50% I would expect the preview to say something like

There were 60 instances that satisfied the conditions of this alert across 1 kubernetes.pod.uids in the last hour.

but instead it says

There were 60 instances that satisfied the conditions of this alert across 10 kubernetes.pod.uids in the last hour.

It feels like we are counting too many UUIDs for the match. When the alert runs, it only matches on one UUID.

[Zacqary]

@simianhacker That's unrelated to this PR, we can file an issue for that. It's currently the expected behavior (telling the user that the alert examined 10 pods total) but we can revisit the language again since it's ambiguous.

[simianhacker]

LGTM