Add reflection-free Jackson deserialization to guide

[rolfedh]

Add information about reflection-free Jackson deserialization to the guide.

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[rolfedh]

Hi @mariofusco,
I've put together a rough draft for you to review.
I wrote this draft based on logical guesswork and assumptions rather than concrete facts, so I'd really appreciate your help in refining it for accuracy.
Thanks in advance!

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[rolfedh]

@mariofusco We'll update this documentation after the release note is finalized.

[rolfedh]

Hi @mariofusco,

I've updated the community docs to align with the release note you approved. Thanks for your review!

[quarkus-bot]

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It should be safe to merge provided you have a look at the other checks in the summary.