feat: add support for using parallel to restore apps

By using parallel, we take advantage of the fact that a server may have multiple cores, thus enabling restores to complete faster.

Refs #2463

plugins/ps/subcommands/restore

@@ -7,6 +7,12 @@ source "$PLUGIN_AVAILABLE_PATH/ps/functions"
 ps_restore_cmd() {
   declare desc="starts all apps with DOKKU_APP_RESTORE not set to 0 via command line"
   local cmd="ps:restore"
+
+  if which parallel > /dev/null 2>&1; then
+    dokku_apps | parallel dokku ps:start
+    return
+  fi
+
   for app in $(dokku_apps); do
     local DOKKU_APP_RESTORE=$(config_get "$app" DOKKU_APP_RESTORE || true)
     if [[ $DOKKU_APP_RESTORE != 0 ]]; then