Add an Application view

### Problem

Mentioned on Discord woth Alexia/@cyrneko :)
So a list of processes is a bit confusing : My app is misbehaving, which process do i kill ? How much RAM in total does it uses ? What is mktcnsyscpio86l-so ? Is it dangerous ? Edible ? Where am i ?

Considering there is also no exposed way to stop an application running in the background, it is also very likely the user may want to stop running apps through Monitor too

### Proposal

A tab focused on currently running, user-level, applications : Discord, Firefox, Libreoffice...
but maybe not Dock or Wingpanel or any system process - as someone with the adequate knowledge to play with that may want to target the process.

I think Cyrneko mentioned SystemD exposed currently running apps ?
else since most of these apps are flatpaks maybe there is a portal for that ?

### Prior Art (Optional)

_No response_