Define PG_LOGICAL_DIR for path pg_logical/ in data folder
This is similar to
2065ddf5e34c, but this time for pg_logical/ itself
and its contents, like the paths for snapshots, mappings or origin
checkpoints.
Author: Bertrand Drouvot
Reviewed-by: Ashutosh Bapat, Yugo Nagata, Michael Paquier
Discussion: https://postgr.es/m/ZryVvjqS9SnV1GPP@ip-10-97-1-34.eu-west-3.compute.internal