Update env.sample variables

[marthamareal]

• Add the following to the env sample
  • CELERY_BEAT_SCHEDULER=celery.beat:PersistentScheduler`
  • DEFAULT_MAX_UPLOAD_SIZE=5368709120
  • DEFAULT_MAX_PARALLEL_UPLOADS_PER_USER=5
• Remove
  • CACHE_BUSTING_MEDIA_ENABLED

[giohappy]

@marthamareal do we need CELERY_BEAT_SCHEDULER. Its default is already that, and this isn't something we usually need to change in a project. In any case, if we need to change it, we can always add it to the specific project.

I'm fine with the other two, since they can be something useful to configure per project.