DuckDNS: Fixes cron issues with dehydrated

[ludeeus]

Description:

Moves the cron job from the crontab of the homeassistant user and ensure that the script are run from the correct directory.
Related issue (if applicable): Fixes #180

Checklist (Required):

• The code change is tested and works locally.
• The code is compliant with Contributing guidelines

If pertinent:

• Script has validation check of the job.
• [N/A] Created/Updated documentation at /docs

[Landrash]

Looks great 👍