feat: Update backend/Dockerfile - node:20 --> node:22

Signed-off-by: Mathieu Benoit <mathieu-benoit@hotmail.fr>

packages/create-app/templates/next-app/packages/backend/Dockerfile

@@ -12,7 +12,7 @@
 # Alternatively, there is also a multi-stage Dockerfile documented here:
 # https://backstage.io/docs/deployment/docker#multi-stage-build
 
-FROM node:20-bookworm-slim
+FROM node:22-bookworm-slim
 
 # Set Python interpreter for `node-gyp` to use
 ENV PYTHON=/usr/bin/python3