Ability to set the timezone cron/ofelia will run in

I can't see any way to set the timezone that the cron/ofelia container is using.

For other containers, i.e. `php`, I can set this in `docker-compose-custom.yml`, i.e.

```yaml
version: '3.5'

services:

php:
environment:
- TZ=Australia/Melbourne
volumes:
- "/etc/timezone:/etc/timezone:ro"
- "/etc/localtime:/etc/localtime:ro"
```

There should be some way to do this for the cron/ofelia container, since [this Ofelia ticket](https://github.com/mcuadros/ofelia/issues/96) suggests that it does respect `TZ` environment variable if set.

My server is in `Australia/Melbourne`, as are most of the containers - except for `ee-cron-scheduler` which appears to still be in `UTC+0`, which is lame as I'd like everything to be using the same timezone.

Hope there is a way!

Comienza inspeccionando docker-compose-custom.yml y la configuración del servicio ee-cron-scheduler para ver cómo está definido el contenedor cron/ofelia. Compara sus ajustes relacionados con la zona horaria con el ejemplo del servicio PHP y verifica después que los trabajos programados usen la zona horaria configurada Australia/Melbourne en lugar de UTC.

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