add release notes for v9.3.6 and v9.4.3

[lahsivjar]

As it says on the tin. Additionally, also adds the missing changelogs for v9.3.5 and v9.4.2

[prodsecmachine]

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[github-actions]

🤖 GitHub comments

Just comment with:

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[github-actions]

🔍 Preview links for changed docs

• docs/release-notes/index.md

[github-actions]

✅ Elastic Docs Style Checker (Vale)

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[mergify]

This pull request does not have a backport label. Could you fix it @lahsivjar? 🙏
To fixup this pull request, you need to add the backport labels for the needed
branches, such as:

• backport-8.19 is the label to automatically backport to the 8.19 branch.
• backport-9./d is the label to automatically backport to the 9./d branch. /d is the digit.
• backport-active-all is the label that automatically backports to all active branches.
• backport-active-9 is the label that automatically backports to all active minor branches for the 9 major.

[mergify]

Tick the box to add this pull request to the merge queue (same as @mergifyio queue).

• Queue this pull request