[8.12](backport #40508) [aws] Update max_number_of_messages doc

[mergify]

Proposed commit message

This PR is to update the documentation for max_number_of_messages to inform users to keep default 5 for this parameter and use the Balanced or Optimized for Throughput presets in the Performance tuning settings to tune your Elastic Agent performance.

This is a followup change after #40231.

Checklist

• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have made corresponding change to the default configuration files
• I have added tests that prove my fix is effective or that my feature works
• I have added an entry in CHANGELOG.next.asciidoc or CHANGELOG-developer.next.asciidoc.

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This is an automatic backport of pull request #40508 done by [Mergify](https://mergify.com).

[mergify]

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	both modified:   x-pack/filebeat/docs/inputs/input-aws-s3.asciidoc

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