Add entity severity as a Risk Insights notification trigger condition

[jenny-park-dd]

What does this PR do? What is the motivation?

Risk Insights notification rules now support setting the trigger condition based on entity severity, in addition to the existing numeric risk score value. Previously, notification conditions supported only a numeric risk score threshold.

This updates step 3 of Configure notifications for Risk Insights to document both options, so users can configure conditions using the same severity labels they see during entity triage.

Merge instructions

Ready to merge.

Additional notes

• The page already documents severity levels in the Entity severity thresholds section, which is what the in-app See entity severity breakdown by risk score link points to. This change cross-links to that section rather than restating the levels inline.
• Existing threshold-based notification rules continue to work without changes, so no migration guidance is needed.
• Available in all regions except GovCloud. The page already carries a site-region notice excluding gov,gov2 from notification rules, so no additional region gating is required.
• No image changes in this PR.
• The es translation of this page is untouched and handled by the localization pipeline.

🤖 Generated with Claude Code

[github-actions]

Preview links (active after the build_preview check completes)

Modified Files

• https://docs-staging.datadoghq.com/jenny.park/risk-insights-severity-notification-conditions/security/cloud_siem/triage_and_investigate/entities_and_risk_scoring