Add 'console cache:warmup' in boot script

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there is an issue here: Heroku expects the app to bind on $PORT within 60 seconds, otherwise it considers it as a failure (boot timeout). But the cache warmup can be longer than that (it is even the goal, to make the heavy cacheable work there instead of during a web request).
I found a workaround by doing the warmup after launching nginx but it could cause some issues for the first request if it comes before the warmup is completed