[8.18] [ESS][8.18] Editing, exporting, and importing prebuilt rules (backport #6563)

[mergify]

Description

Partially addresses #5061 by providing docs for editing, exporting, and importing prebuilt rules (customized and non-customized). Docs for updating customized prebuilt rules are at #6568.

Twin 9.0 and Serverless PR: elastic/docs-content#893

Previews

• Modify existing rules settings: Made a few changes to this section:
  • Added requirements to the start of the section to explain subscription needs.
  • Updated instructions for editing single rules
• Export and import rules: Made the following changes:
  • Added requirements to the start of the section to explain subscription needs for importing and exporting custom and prebuilt rules.
  • Split up the instructions for importing and exporting rules to make the content more findable and readable
  • Added instructions for exporting individual rules

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    This is an automatic backport of pull request [ESS][8.18] Editing, exporting, and importing prebuilt rules #6563 done by Mergify.

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