Fix cron: add cron task only once and start cron service

[YannickR26]

Fix:

• the cron service was not started at startup
• allows to leave the environment variable DOLI_CRON at 1

[tuxgasy]

If you change DOLI_CRON_KEY or DOLI_CRON_USER, the cron task will not be updated.

[YannickR26]

Yes, its true, we can update the cron task at each run if you prefer ?

[tuxgasy]

Currently, the cron file is already regenerated at each run.

[YannickR26]

ok, I updated the docker-run.sh file to check the environment variables and create the cron job at each run.