feat: enhance .env.example with cluster hostname support and update start-nodes.sh to replace environment variables

selenium-standalone-stack/start-nodes.sh

@@ -77,8 +77,13 @@ echo "Starting $NUMBER Selenium nodes"
 
 for NB in $(seq 1 "$NUMBER"); do
     NODE_NAME="selenium-${HOST}-instance-${NB}"
-    
 
+    # Replace variables in the environment file
+    TEMP_ENV_FILE=$(mktemp)
+    while IFS= read -r line; do
+        eval "echo \"$line\""
+    done < "$ENV_FILE" > "$TEMP_ENV_FILE"
+    ENV_FILE="$TEMP_ENV_FILE"
 
     echo "Starting Selenium node n°$NB"
     docker run --rm \