The usual flow of updating the upgrade.html docs is to first do it in apache/kafka/trunk, then cherry-pick to the relative release branch and then copy into the kafka-site repo.
It seems like this was not done with a few commits updating the 3.6.1, 3.5.2 and 3.5.1, resulting in kafka-site's latest upgrade.html containing content that isn't here. This was caught while we were adding the 3.7 upgrade docs.
This patch reconciles both files by taking the extra changes from kafka-site and placing them here. This was done by simply comparing a diff of both changes and taking the ones that apply
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