Missing configuration sections since 1.5 docs

It seems that during the merge of FLINK-8475, some of the content from the TM options didn't make it into the new doc generators, e.g. the notes in taskmanager.memory.preallocate. Before commit eaff4da15b, there were several sections with introduction, meaningful summary of important settings (not just an alphabetical list) and the option texts actually also contained some more information than the new descriptions.

I'd like to see those back again, in particular the (advanced) managed memory configuration notes for batch users.