Copying php in a volume make the init and upgrades very slow

[tcoupin]

The source code is located at /usr/src/nextcloud in the image and the entrypoint script copy it to /var/www/html.

In a high availability environment, it's necessary to share the /var/www/html between containers so you have to store it on NFS like storages who are not very fast. During initialization or upgrade, the entrypoint copy more that 25k files and it's very very slow.

As I said at https://github.com/nextcloud/helm/issues/10#issuecomment-2372067055, I use a customized image who share only folders who need to be writable by several containers using symlink.

This is potentially a big PR so I would like to know if you are interested before starting.