Split audit event streaming documentation into multiple pages

What does this MR do?

While reviewing: !122898 (merged), it become clear that the audit event streaming feature has outgrown a single page.

This MR splits it into three pages:

• A general and UI-focussed page, which is a good place to start.
• A GraphQL API-focussed page, which some people might use but which is more advanced.
• An examples page, because it's a lot of content and needs somewhere else to go.

Results:

• Before: https://docs.gitlab.com/ee/administration/audit_event_streaming.html
• After (main page and UI): https://main-ee-123336.docs.gitlab-review.app/ee/administration/audit_event_streaming/index.html
• After (examples): https://main-ee-123336.docs.gitlab-review.app/ee/administration/audit_event_streaming/examples.html
• After (GraphQL API): https://main-ee-123336.docs.gitlab-review.app/ee/administration/audit_event_streaming/graphql_api.html

Related issues

Somewhat related to: https://gitlab.com/gitlab-com/gitlab-OKRs/-/work_items/3102.

Author's checklist

• Optional. Consider taking the GitLab Technical Writing Fundamentals course.
• Follow the:
  • Documentation process.
  • Documentation guidelines.
  • Style Guide.
• If you're adding or changing the main heading of the page (H1), ensure that the product tier badge is added.
• If you are a GitLab team member, request a review based on:
  • The documentation page's metadata.
  • The associated Technical Writer.

If you are a GitLab team member and only adding documentation, do not add any of the following labels:

• ~"frontend"
• ~"backend"
• ~"type::bug"
• ~"database"

These labels cause the MR to be added to code verification QA issues.

Reviewer's checklist

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If you aren't sure which tech writer to ask, use roulette or ask in the #docs Slack channel.

• If the content requires it, ensure the information is reviewed by a subject matter expert.
• Technical writer review items:
  • Ensure docs metadata is present and up-to-date.
  • Ensure the appropriate labels are added to this MR.
  • Ensure a release milestone is set.
  • If relevant to this MR, ensure content topic type principles are in use, including:
    • The headings should be something you'd do a Google search for. Instead of Default behavior, say something like Default behavior when you close an issue.
    • The headings (other than the page title) should be active. Instead of Configuring GDK, say something like Configure GDK.
    • Any task steps should be written as a numbered list.
    • If the content still needs to be edited for topic types, you can create a follow-up issue with the docs-technical-debt label.
• Review by assigned maintainer, who can always request/require the reviews above. Maintainer's review can occur before or after a technical writer review.