Add missing update script

templates/update-opensearch-plugins.j2

@@ -0,0 +1,35 @@
+#!/bin/sh
+# {{ ansible_managed }}
+
+set -eu
+
+OPENSEARCH_BIN_PATH=/usr/share/opensearch/bin
+OPENSEARCH_SERVICE=opensearch.service
+PLUGINS=(
+    ingest-attachment
+)
+
+ACTION="${1:-help}"
+
+case "$ACTION" in
+    purge)
+        for plugin in "${PLUGINS[@]}"; do
+            $OPENSEARCH_BIN_PATH/opensearch-plugin remove $plugin --batch
+        done
+        systemctl restart $OPENSEARCH_SERVICE
+        ;;
+    install)
+        for plugin in "${PLUGINS[@]}"; do
+            $OPENSEARCH_BIN_PATH/opensearch-plugin install $plugin --batch
+        done
+        systemctl restart $OPENSEARCH_SERVICE
+        ;;
+    help)
+        echo "Syntax:  $(basename "$0")  { purge | install | help }"
+        echo
+        ;;
+    *)
+        "$0" help >&2
+        exit 1
+        ;;
+esac