[8.x] Add Fleet & Agent 8.16.2 Release Notes (backport #1538)

[mergify]

This adds the 8.16.2 Fleet & Elastic Agent Release Notes:

• No new Fleet contents in Kibana Release Notes PR
• No new Fleet Server contents in BC1 changelog
• Elastic Agent contents from BC1 changelog
• The note about Wolfi images is requested in https://github.com/elastic/dev/issues/2926

Closes: #1528

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This is an automatic backport of pull request #1538 done by [Mergify](https://mergify.com).

[github-actions]

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