Enable fsync=on by default in gpAux/gpdemo/gpdemo-defaults.sh

Previously, fsync was set to off by default unless NUM_PRIMARY_MIRROR_PAIRS was zero or fsync was explicitly set to on.
This change ensures that fsync is always on, improving data durability and consistency by default in the demo setup.

Author: yjhjstz

gpAux/gpdemo/gpdemo-defaults.sh

@@ -16,7 +16,7 @@ if [ "${NUM_PRIMARY_MIRROR_PAIRS}" -eq "0" ]; then
   BLDWRAP_POSTGRES_CONF_ADDONS="fsync=on ${BLDWRAP_POSTGRES_CONF_ADDONS}"  # always enable fsync if singlenode
 fi
 if [[ ! ${BLDWRAP_POSTGRES_CONF_ADDONS} == *"fsync=on"* ]]; then
-  BLDWRAP_POSTGRES_CONF_ADDONS="fsync=off ${BLDWRAP_POSTGRES_CONF_ADDONS}" # only append fsync=off if it doesn't contains fsync=on
+  BLDWRAP_POSTGRES_CONF_ADDONS="fsync=on ${BLDWRAP_POSTGRES_CONF_ADDONS}" # always fsync=on
 else
   BLDWRAP_POSTGRES_CONF_ADDONS="${BLDWRAP_POSTGRES_CONF_ADDONS}"
 fi