[Request] Update AI Assistant Docs

[Charelzard]

Description

What: Update the following AI Assistant Docs: https://www.elastic.co/guide/en/security/current/security-assistant.html.
How: Use this link to see what the page should look like. All highlighted items are new content and need to be included in messaging. Feel free to set up a call if needed. https://docs.google.com/document/d/1Z2yxxtIc9lmnqAyu-u0iuXniNs0YajbcdrLo_6cQk7w/edit?usp=sharing

Background & resources

N/A

Which documentation set does this change impact?

ESS and serverless

ESS release

8.16

Serverless release

N/A

Feature differences

N/A

API docs impact

N/A

Prerequisites, privileges, feature flags

N/A

[Charelzard]

FYI @benironside and @jamesspi