[IMPROVEMENT] Allow selecting multiple rows in main grid.

### 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 improvement 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 improvement 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

## Existing
The main grid allows a user to select a row, click and make selected.
There is no mechanism to multi select (typically click a row, shift click another group to select the between group.

## Improvement
Provide the ability to select a group of rows using CTRL-Click or SHIFT-Click to group a collection of rows.

### Describe how this improvement could help users

More flexibility selecting packages/updates