The current path of the `$GITEA_APP_INI` configuration file makes the
forgejo application reset every time the container is restarted, unless
a specific volume for this file is created. Consider the following:
* This quirk is not documented
* All configuration data resides in `/var/lib/gitea`
* The custom configuration path defaults to `/var/lib/gitea/custom/conf`
(see `forgejo -h`)
* Containers mounting the volume `-v /foo/bar:/var/lib/gitea` already
have this file available to modify. Another volume shouldn't be
required
* Containers using named volumes can use `docker cp` to modify the file
inside the volume, if desired
For these reasons, it makes more sense to use the default path for
`$GITEA_APP_INI` rather than require users to create a dedicated volume
for the file. Revert it back to its default while maintaining backwards
compatibility (users can update by simply moving the file to the new
path).
