Update to php 8.1

[nijave]

Hi, not sure if this interests you but I made some tweaks to logging and updated to PHP 8.1

Summary of changes:

• Remove cron dependency so container will run as non-root
• Split npm pieces into an additional stage
• Add missing php extensions (tidy)
• Send logs to stdout/stderr

[MatthK]

To be honest, I am not that much of a docker specialist to perfectly understand all the changes. I trust that it is beneficial.