feat: create script structure from doc

Create update script to avoid mistakes when updating manually Humhub based on official update documentation : https://docs.humhub.org/docs/admin/updating

ToDo :

• Create vars
• Check parameters function to avoid empty vars
• Finish each function
• Optionnal remove backup
• Finish script init
• Fix shellcheck errors
• Add checksum Check
• Test locally
• Test on rezo
• Doc it ! 📝