feat: prepare ground for config directory changes

config

@@ -4,6 +4,7 @@ export POSTGRES_IMAGE_VERSION=${POSTGRES_IMAGE_VERSION:="9.6.4"}
 export POSTGRES_ROOT=${POSTGRES_ROOT:="/var/lib/dokku/services/postgres"}
 
 export PLUGIN_COMMAND_PREFIX="postgres"
+export PLUGIN_CONFIG_ROOT="${DOKKU_LIB_ROOT}/config/${PLUGIN_COMMAND_PREFIX}"
 export PLUGIN_DATA_ROOT=$POSTGRES_ROOT
 export PLUGIN_DATASTORE_PORTS=(5432)
 export PLUGIN_DATASTORE_WAIT_PORT=5432