[8.17](backport #42306) x-pack/filebeat/docs - document gzip S3 object handling

[mergify]

Proposed commit message

Document how compressed objects are handled by the aws-s3 input.

---

This is an automatic backport of pull request #42306 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of 7fd2d46 has failed:

On branch mergify/bp/8.17/pr-42306
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	both modified:   x-pack/filebeat/docs/inputs/input-aws-s3.asciidoc

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[botelastic]

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