The Docker image is used in the initialization process, to copy
everything in the custom folder to the Gitea data dir (mounted as a
persistent volume). It is built using Packer and is based on the busybox
image, so we can use its minimalist shell system to copy files and set
permissions
For now it is only labels, but adding anything supported will work
(robots.txt, public files, templates, etc)
The content will be copied to the /data/gitea/ folder that is a mounted
persistent volume
https://docs.gitea.io/en-us/customizing-gitea/