Add a more granular container detection
Replace is_in_container by get_container_info
Currently detect Official container (once they update a version with a tagfile) and LinuxServer container
All other container are marked as Unknown
Report two field :
- container_type ( none | Official | LinuxServer | Unknown
- container_version ( build Version number like 16.2.0a, only reported if Official container is detected )
Append info on PHP_OS in the template of `admin/maintenance_env.php` and in `include/functions.inc.php` -> `send_piwigo_infos()`
Detection works by checking if PHP is running on Linux then check if PID2 is kthreadd
Kthreadd is useless in a container so PID2 should not exist of be another process
If unable to read /proc/2/sched for some reason, assume a SELinux restriction and that PHP is not running in a container
`is_in_container()` doesn't differentiate between VMs or bare metal, it only check if PHP is running in a containerized environement via tools like docker or podman
