add opensearch addons

opensearch-nginx-lb/Dockerfile

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+ARG BASE_IMAGE=nginx:stable
+FROM ${BASE_IMAGE}
+COPY rootfs/ /

opensearch-nginx-lb/config.json

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+{
+  "name": "OpenSearch NGINX Load Balancer",
+  "version": "1.0.0",
+  "slug": "opensearch-nginx-lb",
+  "description": "NGINX load balancer for OpenSearch coordinator nodes.",
+  "arch": [
+    "amd64",
+    "armv7",
+    "arm64"
+  ],
+  "startup": "services",
+  "boot": "auto",
+  "host_network": true,
+  "map": [
+    [
+      "config",
+      "./config",
+      "rw"
+    ]
+  ],
+  "options": {
+    "lb_port": 9200,
+    "coordinator_nodes": [
+      "os-coord-1",
+      "os-coord-2"
+    ]
+  },
+  "schema": {
+    "lb_port": "int",
+    "coordinator_nodes": [
+      "list",
+      [
+        "str"
+      ]
+    ]
+  },
+  "ports": {
+    "9200/tcp": 9200
+  }
+}

opensearch-nginx-lb/rootfs/config/nginx.conf

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+events {}
+http {
+    upstream opensearch_coord {
+        server os-coord-1:9200;
+        server os-coord-2:9200;
+    }
+    server {
+        listen 9200;
+        location / {
+            proxy_pass http://opensearch_coord;
+        }
+    }
+}

opensearch-nginx-lb/rootfs/etc/s6-overlay/s6-rc.d/nginx/finish

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+#!/command/execlineb -S0
+# Prevent restart loops; allow clean exit
+exit 0

opensearch-nginx-lb/rootfs/etc/s6-overlay/s6-rc.d/nginx/run

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+#!/command/with-contenv bash
+set -euo pipefail
+echo "[s6-run] Starting NGINX load balancer"
+exec nginx -g 'daemon off;'