[FEAT] Adding the "installed apps" count

### Description

Hi!
I believe it would be beneficial to include the number of apps installed on macOS and Windows in Fastfetch.
This could be implemented through a new module (e.g., `Apps` or `Applications`) or as an option in the custom format within `Packages`.

### Motivation

In my personal use case, the `Command` module is sufficient for retrieving the number of installed apps.
However, I think that many macOS and Windows users install applications instead of packages (or a combination of both) but they may not know how to write that specific command.
Therefore, it might be more user-friendly to incorporate this functionality as a native feature in Fastfetch.

### Additional context

If useful, here is my configuration with the command I use to retrieve the number of apps on macOS. The command I use simply counts the apps displayed in `Spotlight` / `Apps`:
```jsonc
{
"type": "command",
"key": "Apps",
"text": "mdfind \"kMDItemContentType == 'com.apple.application-bundle'\" -onlyin /Applications -onlyin ~/Applications -onlyin /System/Applications | wc -l | xargs"
},
```
I still haven’t found a polished command for Windows but I can share my attempts if needed.

Thank you for considering my suggestion.

Edit: I’ve updated the command above to the "final" version. If you’re interested in previous iterations or alternative approaches, please refer to the comments below.