[FEATURE REQUEST] Option to clear previous "Discover Packages" search when re-navigating to it or creating new window

### 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

Flow 1:

1. Open UniGetUI
2. Search for a package in "Discover Packages" tab
3. Close the window (UniGetUI continues running in the tray)
4. Create a new window by opening UniGetUI from the taskbar / start menu / search / quick launch toolbar

Flow 2:

1. Open UniGetUI
2. Search for a package in "Discover Packages" tab
3. Navigate to the "Software Updates" tab
4. Navigate to the "Discover Packages" tab

Currently, both these flows retain the previous search:

With the proposed option enabled, executing Step 4 of each flow above should clear the search. The user would be presented with this:

### Describe how this new feature could help users

This feature would complement https://github.com/Devolutions/UniGetUI/issues/4550 well. It would allow users to reliably launch UniGetUI then immediately start typing to search for packages.

This allows the user to launch and use UniGetUI to install packages easily without having to reach for the mouse, which is an unnecessary context switch.