add opensearch addons

opensearch-dashboards/rootfs/etc/cont-init.d/20-install-plugins

@@ -0,0 +1,20 @@
+#!/command/with-contenv bash
+set -euo pipefail
+OPTIONS_FILE=/data/options.json
+if [ ! -f "$OPTIONS_FILE" ]; then
+  echo "[cont-init] No options.json, skipping dashboards plugin install"
+  exit 0
+fi
+if ! jq -e '.plugins // [] | length > 0' "$OPTIONS_FILE" >/dev/null 2>&1; then
+  echo "[cont-init] No dashboards plugins configured, skipping"
+  exit 0
+fi
+echo "[cont-init] Installing dashboards plugins from options.json"
+jq -r '.plugins[]' "$OPTIONS_FILE" | while read -r plugin; do
+  echo "[cont-init] Installing dashboards plugin: $plugin"
+  if /usr/share/opensearch-dashboards/bin/opensearch-dashboards-plugin install --allow-root "$plugin"; then
+    echo "[cont-init] Installed dashboards plugin $plugin"
+  else
+    echo "[cont-init] Failed to install dashboards plugin $plugin (continuing)"
+  fi
+done