Support user-level installation on Windows

**Is your feature request related to a problem? Please describe.**
User-level installation of the Windows package is not available. For example, winget shows that no user-level installation is configured:

```
> winget install --scope user StephanDilly.gitui
No applicable installer found; see logs for more details.
```

The .msi installer in the releases page requires admin access.

**Describe the solution you'd like**
Add the ability to install the program for just the current user i.e. in `~\AppData`.

Start by locating the Windows MSI packaging configuration and the release metadata used by winget. Check how the current installer selects its install scope and verify the expected behavior on Windows. Done means winget can install gitui with --scope user into the current user's AppData without requiring administrator access.

Written by the indexing model from the issue text.