[Detection Engine][Exceptions] - Update docs for single and shared exceptions

[nastasha-solomon]

Fixes #3491.

Previews:

• Elastic Security APIs: Refreshed the description for the Detections API since it technically allows users to manage rule exceptions for individual rules
• Detections API: Added endpoints for creating a default exception list and creating exception items for a single rule
• Create a default exception list for a rule: New page that shows how to create an exception list for a single rule (a default exception list)
• Create exceptions for individual rules: New page that shows how to create exception items that you can add to a default exception list
• Create exception container | Request body: Added the rule_default value to the type parameter description. Users would enter this value if they wanted the exception container to hold single-rule exception lists (i.e., the default exception list for a rule).
• Create exceptions used by multiple rules: Made several changes:
  • Updated the title and intro para to show that this endpoint should be used to create exception items that are shared between multiple rules.
  • Added note to the intro that allows users to find docs for creating single rule exception items and exception items created from lists.
  • Fixed or refreshed docs for the following request params: comments, namespace_type, os_types, tags, and list

[github-actions]

Documentation previews:

• ✨ HTML diff
• 📙 Elastic Security Guide

[nastasha-solomon]

Hey, @yctercero! These docs are ready for your review when you have a chance. As you're reviewing the docs, there are questions for you here about finding rule IDs and here about an example request. I was also hoping you could tell me whether the following endpoints could also be used to manage exception items added to rule default lists:

• https://www.elastic.co/guide/en/security/current/exceptions-api-find-exception-items.html
• https://www.elastic.co/guide/en/security/current/exceptions-api-get-item.html
• https://www.elastic.co/guide/en/security/current/exceptions-api-update-item.html
• https://www.elastic.co/guide/en/security/current/exceptions-api-delete-item.html

If they can, I might need to tweak their intros, plus the descriptions for the detections and exception APIs here.

[yctercero]

@caitlinbetz is this still accurate? I know we opened endpoint exceptions up to have less field restrictions, not sure if these still hold.