Re: row filtering for logical replication

The current documentation updates (e.g. in the v61 patch) for the
Row-Filter are good, but they are mostly about syntax changes and
accompanying notes for the new WHERE clause etc. There are also notes
for subscription tablesync behaviour etc.

But these new docs feel a bit like scattered fragments - there is
nowhere that gives an overview of this feature.

IMO there should be some overview for the whole Row-Filtering feature.
The overview text would be similar to the text of the 0001/0002 commit
messages, and it would summarise how everything works, describe the
UPDATE transformations (which currently seems not documented anywhere
in PG docs?), and maybe include a few useful filtering examples.

e.g. Perhaps there should be an entirely new page (section 31 ?)
devoted just to "Logical Replication Filtering" - with subsections for
"Row-Filtering" and "Col-Filtering".

Thoughts?

------
Kind Regards,
Peter Smith.
Fujitsu Australia