feat: move all image names to config file

This allows us to more quickly update the image versions in use for tertiary images.

functions

@@ -80,7 +80,7 @@ service_create_container() {
   echo "$ID" >"$SERVICE_ROOT/ID"
 
   dokku_log_verbose_quiet "Waiting for container to be ready"
-  docker run --rm --link "$SERVICE_NAME:$PLUGIN_COMMAND_PREFIX" dokku/wait:0.4.1 -p "$PLUGIN_DATASTORE_WAIT_PORT" >/dev/null
+  docker run --rm --link "$SERVICE_NAME:$PLUGIN_COMMAND_PREFIX" "$PLUGIN_WAIT_IMAGE" -p "$PLUGIN_DATASTORE_WAIT_PORT" >/dev/null
 
   dokku_log_info2 "$PLUGIN_SERVICE container created: $SERVICE"
   service_info "$SERVICE"