[Request][Serverless & 8.15]: Expandable flyout setting being removed from advanced settings

[nastasha-solomon]

Fixes #5291 by removing docs for the securitySolution:enableExpandableFlyout advanced setting.

ESS previews:

• Configure advanced settings
• View detection alert details

Serverless previews:

• Configure advanced settings
• View detection alert details

[github-actions]

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[nastasha-solomon]

@PhilippeOberti merged elastic/kibana#184169 today, so the change should be included in next week's Serverless release, which is currently scheduled to begin on June 10.

Before I merge this PR, I need to verify that the securitySolution:enableExpandableFlyout advanced setting is no longer visible on the Advanced Settings page in Serverless -- QA and prod envs. It'd also be worth spot-checking areas where the expandable flyout is used, such as Timeline (events and alerts), the Hosts page (host details), and the Users page (user details).

If a backport PR is created (which is very unlikely because the 8.15 docs branch hasn't been cut yet), I'll need to remove Serverless files from the backport PR.

[nastasha-solomon]

I checked the QA server and confirmed that the securitySolution:enableExpandableFlyout setting isn't available on the Advanced Settings page. Today and tomorrow, I'll watch the Kibana release tracker and periodically check our Canary Prod project to see if this change has been promoted.

[mergify]

This pull request is now in conflicts. Could you fix it @nastasha-solomon? 🙏
To fixup this pull request, you can check out it locally. See documentation: https://help.github.com/articles/checking-out-pull-requests-locally/

git fetch upstream
git checkout -b issue-5291-expand-flyout-removed upstream/issue-5291-expand-flyout-removed
git merge upstream/main
git push upstream issue-5291-expand-flyout-removed

[nastasha-solomon]

Validated that the change is available on the Prod Canary Server. Dashboard shows that the promotion to Prod Noncanary is complete too, so can merge tomorrow.

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