RE: Make pgoutput documentation easier to find

Dear Fujii-san,

> The current documentation for pgoutput is buried in the logical streaming
> replication protocol section (in protocol.sgml), and there's no index entry
> for it. This makes it hard to discover and access, for example, when trying
> to look up the options it supports.
>
> I've often struggled to locate this information myself, so I'd like to
> propose moving the pgoutput documentation to the logical decoding section
> and adding an index entry. The attached patch does that. I think this change
> will make it much easier for users to find the relevant details.

Personally considered pgoutput is not the user-facing and extension developers
can dig by themselves, but this is not a huge complaint.
DBA may check their settings via pg_recvlogical, which is a use-case.

I did agree to add new chapter for plugin developers, but it could be done at
different thread.

Since pgoutput can only generate the binary output, it pg_logical_slot_get_changes()
cannot be used with this plugin. I felt this should be also documented.

Another point: test_decoding does not have descriptions for their options neither.
Should we also add as well?

Best regards,
Hayato Kuroda
FUJITSU LIMITED