pgsql: Doc: clarify there's no log_line_prefix in csvlog or jsonlog out

Doc: clarify there's no log_line_prefix in csvlog or jsonlog output.

The documentation didn't make clear that "log_line_prefix" is
not output when "log_destination" is "csvlog" or "jsonlog".

Reported-by: Michael Schönitzer <michael(at)schoenitzer(dot)de>
Author: Laurenz Albe <laurenz(dot)albe(at)cybertec(dot)at>
Co-authored-by: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Discussion: https://postgr.es/m/179032875673.1026201.6950455317699774504@wrigleys.postgresql.org
Backpatch-through: 14

Branch
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REL_14_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/fba35c7c28a567839faba867db0808564c0a66db

Modified Files
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doc/src/sgml/config.sgml | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)