Resize `half` window size

**Is your feature request related to a problem? Please describe.**
- I prefer the half view for my most common use cases. but for the file tree, the left hand side doesn't need to be that wide.
- I have this in my config
```
gui:
windowSize: "half"

```

**Describe the solution you'd like**
- It'd be nice to have a configurable value to set the width of the `half`.
- there already exists `sidePanelWidth: 0.3333 # number from 0 to 1`, but this is not respected by the `half` screen, only the `normal` screen.
- maybe something like `halfSidePanelWidth: ...`

**Describe alternatives you've considered**
Staying in `normal` mode and resizing the left hand side via the `sidePanelWidth` option. But i prefer half

**Additional context**

- related issue: https://github.com/jesseduffield/lazygit/issues/2571

- I'd like to be able to resize the right pane to the size of the red box.