[ENHANCEMENT] Remember last used path for Export settings to a local file

### Please confirm these before moving forward

- [X] I have searched for my feature proposal and not found a work-in-progress/duplicate/resolved/discarded issue.
- [X] This improvements refers to an existing feature. If you want to suggest a new feature, please use [this template](https://github.com/marticliment/WingetUI/issues/new?assignees=marticliment&labels=new-feature&projects=&template=feature-request.yml&title=%5BFEATURE+REQUEST%5D+%28Enter+your+description+here%29)
- [X] This improvements is not a bug. If you want to report a bug, please use [this template](https://github.com/marticliment/WingetUI/issues/new?assignees=marticliment&labels=bug&projects=&template=bug-issue.yml&title=%5BBUG%5D+%28Enter+your+description+here%29)

### Describe the improvement

See title.

### Describe how this improvement could help users.

Each time we export WingetUI's settings to a file, we have to browse to our preferred save path. If this path was remembered, exporting would be much quicker in most cases. This could also be implemented for importing. If the path doesn't exist, default to the user's home (as currently occurs).

**Edit:** Other places where paths are set could also use this feature, for instance the backup location for "installed packages" JSONs (which automatically run on login).