[Internal][8.18 & 8.19][Security]: Fix bugs in alert suppression docs and apply improvements

[nastasha-solomon]

Description

Need to do the following:

• Fix the outdated images in the 8.18 and 8.19 alert suppression docs (alert-suppression-options.png and suppressed-alerts-details.png) which still had the tech preview labels. Suppression was GA for all rules types in 8.18.
• Apply the content improvements that were also added in [Security][9.2 & Serverless]: New advanced setting that controls suppression window behavior #2735.

Resources

N/A

Which documentation set does this change impact?

Elastic On-Prem and Cloud (all)

Feature differences

N/A

What release is this request related to?

8.18

Serverless release

N/A

Collaboration model

The documentation team

Point of contact.

Main contact: @approksiu @yctercero

Stakeholders: @approksiu @yctercero

[nastasha-solomon]

@approksiu the 8.18 and 8.19 docs should have the updated screenshots and content improvements in another hour or so when the public docs finish rebuilding.

cc: @yctercero