Copy-edit docs for logical replication column lists

Copy-edit docs for logical replication column lists

There was a excessive structure, leading to somewhat disorganized
presentation of the information. Remove a few tags and reorder
paragraphs to make the text flow more easily.  Also, reword some of it
to be more concise.

The bit about column list combination is not modified, other than to
remove an uninteresting (and IMO confusing and wrong) paragraph; I
intend to deal with it differently afterwards.

Backpatch to 15.

Discussion: https://postgr.es/m/20220913121138.yn7ekkfysxzhkm2u@alvherre.pgsql