The recent refactoring done in ac7c807 makes this move possible and
simple, as this just moves some code around. This reduces the size of
elog.c by 7%.
Author: Michael Paquier, Sehrope Sarkuni
Reviewed-by: Nathan Bossart
Discussion: https://postgr.es/m/CAH7T-aqswBM6JWe4pDehi1uOiufqe06DJWaU5=X7dDLyqUExHg@mail.gmail.com
simply moves the routines related to csvlog into their own file
