[FEATURE REQUEST] Setting to make Notifications Persistent

### Please confirm these before moving forward.

- [x] I have searched for my feature proposal and have not found a work-in-progress/duplicate/resolved/discarded issue.
- [x] This proposal is a completely new feature. If you want to suggest an improvement or an enhancement, please use [this template](https://github.com/Devolutions/UniGetUI/issues/new?labels=enhancement&projects=&template=enhancement-improvement.yml&title=%5BENHANCEMENT%5D+%28Enter+your+description+here%29).

### Describe the new feature

I would like the ability to set UniGet UI's notifications to persist until acknowledged.

Currently `scenario="default"` [is hardcoded on every toast UniGetUI raises](https://github.com/Devolutions/UniGetUI/blob/efa252e1ec04689abb140d7e422891cbd939fad0/src/UniGetUI.Avalonia/Infrastructure/Win32ToastNotifier.cs#L114), so all notifications auto-dismiss after the Windows's normal timeout (a few seconds, by default).

I believe this could be added by giving the option to change notifications to optionally use `scenario="reminder"`
Ideally, this would be an option the user could adjust under `Notification preferences` in settings.

### Describe how this new feature could help users

When there are updates needed, I prefer to know in a way that is impossible to ignore, and I imagine there might be others out there who feel the same way.

Start with src/UniGetUI.Avalonia/Infrastructure/Win32ToastNotifier.cs at the linked toast construction around line 114, then trace the Notification preferences settings. Check how the current default scenario and Windows timeout are handled. Done means users can choose persistent notifications and the selected preference affects UniGetUI toasts until they are acknowledged.

Written by the indexing model from the issue text.