[Docs] Increase vm.max_map_count suggested value (attempt 2)

[shainaraskas]

We want to recommend a higher vm.max_map_count for Elasticsearch environments - additional context in issue

Changes made:

• bumped the recommended max_map_count from 262144 to 1048576 in docs and examples, with the exception of GKE Autopilot
• Documented GKE Autopilot exception in recommendations
• bumped NOTICE.txt to satisfy CI

recreation of #8971 (couldn't be merged because it wasn't from a fork)

What issues does this PR fix?
Part of https://github.com/elastic/docs-content-internal/issues/592

[prodsecmachine]

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