Update input-kafka.asciidoc

[nimarezainia]

Making the suggested changes where ever the version was mentioned in this file.

What does this PR do?

Clarifying the Kafka versions supported.

Why is it important?

#29310

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.

Related issues

#29310

[elasticmachine]

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• Start Time: 2022-05-19T20:42:28.040+0000

• Duration: 19 min 7 sec

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[elasticmachine]

Pinging @elastic/elastic-agent-data-plane (Team:Elastic-Agent-Data-Plane)

[jlind23]

Closing this as it is for now outdated and hasn't been worked on for quite some time. Feel free to reopen it if need be.