[PHP] Continuous Integration / Clean code

[docjyJ]

Is your feature request related to a problem? Please describe.

Nextcloud all in one is an old project with lots of features. The idea is to update its code by taking advantage of psalm's type checking, a new feature introduced by PHP.

Describe the solution you'd like

Use: https://github.com/nextcloud/coding-standard
Go to level 1: https://psalm.dev/docs/running_psalm/error_levels/
See: https://docs.nextcloud.com/server/latest/developer_manual/digging_deeper/continuous_integration.html

Describe alternatives you've considered

Additional context

• AIO-interface: add Unhealthy container state #5307
• Update Configuration management #5328
• aio-interface: Improve psalm #5369 (before Clean code, resolve psalm type error #5308)
• Add nextcloud/coding-standard dependency #5370
• Add docker in readme #5371
• AIO-interface: Use enum instead of interface for state #5372
• aio-interface: improve constructor #5389
• feat: toggle submit button based on unsaved changes #5576

I will add more info to this issue when I have time.