Dockerfile: Listen to any addresses instead of localhost, fixes #4682

Dockerfile

@@ -43,7 +43,7 @@ COPY --from=builder /app/.next/server ./.next/server
 EXPOSE 3000
 
 CMD if [ -n "$PROXY_URL" ]; then \
-    export HOSTNAME="127.0.0.1"; \
+    export HOSTNAME="0.0.0.0"; \
     protocol=$(echo $PROXY_URL | cut -d: -f1); \
     host=$(echo $PROXY_URL | cut -d/ -f3 | cut -d: -f1); \
     port=$(echo $PROXY_URL | cut -d: -f3); \