feat(infra): add second OPC UA server instance (opcua2) on port 50010

Enables multi-server testing with independent state. Both instances
share the same nodes.json tag config. Updated all infra documentation.

infra/docker-compose.yml

@@ -20,6 +20,27 @@ services:
       - scadalink-net
     restart: unless-stopped
 
+  opcua2:
+    image: mcr.microsoft.com/iotedge/opc-plc:latest
+    container_name: scadalink-opcua2
+    ports:
+      - "50010:50010"
+      - "8081:8080"
+    volumes:
+      - ./opcua/nodes.json:/app/config/nodes.json:ro
+    command: >
+      --autoaccept
+      --unsecuretransport
+      --sph
+      --sn=5 --sr=10 --st=uint
+      --fn=5 --fr=1 --ft=uint
+      --gn=5
+      --nf=/app/config/nodes.json
+      --pn=50010
+    networks:
+      - scadalink-net
+    restart: unless-stopped
+
   ldap:
     image: glauth/glauth:latest
     container_name: scadalink-ldap