Docs workflow test: Add 'queue.mem.datatype' setting

[kilfoyle]

This adds the pretend new Kafka output setting queue.mem.datatype to the Fleet and Agent Guide.

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[kilfoyle]

@kilfoyle Thanks for opening this!
Two questions:

• Should this be backported into the 8.14 docs?
• This updates the Fleet Kafka output settings page. Should the standalone Elastic Agent Kafka output settings page also be updated?

[karenzone]

LGTM