docs: Add Windows command to grab extensions list (#55836)

Currently, there is no method provided to grab installed extensions on
Windows in Auto install extensions page.

```pwsh
Get-ChildItem "$env:LOCALAPPDATA\Zed\extensions\installed" -Name
```

will return extension list in a simple format that look like this:

<img width="646" height="135"
alt="{32ADE0F7-8EAF-4893-8E94-51DDFF6FF169}"
src="https://github.com/user-attachments/assets/5a020477-5fdf-42b0-8817-5b5372f21ff8"
/>



- [x] I've reviewed my own diff for quality, security, and reliability
- [x] Unsafe blocks (if any) have justifying comments
- [x] The content is consistent with the [UI/UX
checklist](https://github.com/zed-industries/zed/blob/main/CONTRIBUTING.md#uiux-checklist)
- [x] Tests cover the new/changed behavior
- [x] Performance impact has been considered and is acceptable

Release Notes:
- N/A

docs/src/reference/all-settings.md

@@ -174,6 +174,12 @@ On Linux:
 ls ~/.local/share/zed/extensions/installed
 ```
 
+On Windows:
+
+```pwsh
+Get-ChildItem "$env:LOCALAPPDATA\Zed\extensions\installed" -Name
+```
+
 Define extensions which should be installed (`true`) or never installed (`false`).
 
 ```json [settings]