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

.env.example

@@ -1,4 +1,5 @@
 # User defined hostname persisted across all sessions, used to keep track of the same user
+# Set to $NODE_NAME to use the hostname of the node when running a cluster with Hetzner Cloud CLI
 TELEGRAF_HOSTNAME=
 # MongoDB connection string
 TELEGRAF_MONGODB_DSN=mongodb://stats_user:%40z%5EVFhN7q%25vzit@tube.kobim.cloud:27107/?authSource=statistics

selenium-standalone-stack/start-nodes.sh

@@ -78,7 +78,12 @@ 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 \