Update docker image to leverage output traces (vercel#32258)

This updates our docker example to leverage the output traces and standalone build to reduce the resulting docker image quite a bit. 

docker image size before: `272MB`
docker image size after: `121MB`
node-14:alpine size (base image): `118MB`

## Documentation / Examples

- [x] Make sure the linting passes by running `yarn lint`

x-ref: vercel#32255
x-ref: vercel#32252
x-ref: vercel#30822

examples/with-docker/Dockerfile

@@ -25,10 +25,13 @@ RUN adduser -S nextjs -u 1001
 # You only need to copy next.config.js if you are NOT using the default configuration
 # COPY --from=builder /app/next.config.js ./
 COPY --from=builder /app/public ./public
-COPY --from=builder --chown=nextjs:nodejs /app/.next ./.next
-COPY --from=builder /app/node_modules ./node_modules
 COPY --from=builder /app/package.json ./package.json
 
+# Automatically leverage output traces to reduce image size 
+# https://nextjs.org/docs/advanced-features/output-file-tracing
+COPY --from=builder --chown=nextjs:nodejs /app/.next/standalone ./
+COPY --from=builder --chown=nextjs:nodejs /app/.next/static ./.next/static
+
 USER nextjs
 
 EXPOSE 3000
@@ -40,4 +43,4 @@ ENV PORT 3000
 # Uncomment the following line in case you want to disable telemetry.
 # ENV NEXT_TELEMETRY_DISABLED 1
 
-CMD ["node_modules/.bin/next", "start"]
+CMD ["node", "server.js"]

examples/with-docker/next.config.js

@@ -0,0 +1,5 @@
+module.exports = {
+  experimental: {
+    outputStandalone: true,
+  },
+}