[8.14] [Detection Engine][Exceptions] - Update docs for single and shared exceptions (backport #4021)

[mergify]

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

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This is an automatic backport of pull request #4021 done by [Mergify](https://mergify.com).

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