[Security][9.2 & Serverless]: New advanced setting that controls suppression window behavior

[nastasha-solomon]

NOTE TO SELF (09/10/25): Sync with @denar50 about feature flag when I'm back.

Contributes to #2526 by documenting the new securitySolution:suppressionBehaviorOnAlertClosure advanced setting. (preview)

Also made the following changes:

• Moved pre-reqs for using alert suppression to the section that has instructions for using it. This placement seems more appropriate. Also made light revisions to wordy steps. (preview)
• Moved that giant note about suppressing fields with multiple values to a dedicated section with the goal of streamlining the instructions for configuring suppression. (preview)
• Added a new section that explained the impact of closing alerts that were generated by alert suppression. (preview)
• Resized a few images that looked disproportionately large.

NOTE: Made the same content improvements to the 8.x suppression docs in elastic/security-docs#7083

[github-actions]

🔍 Preview links for changed docs

• solutions/security/detect-and-alert/suppress-detection-alerts.md
• solutions/security/get-started/configure-advanced-settings.md

[approksiu]

Awesome work!

[denar50]

LGTM!

[nastasha-solomon]

Checked the Serverless prod project and verified the advanced setting was available. Merging PR now.