Be less strict about the search term

## What Happened

After I sideloaded an app from Flathub, I'm able to search for other Flatpak apps in AppCenter. However, when searching for "Libre Office" or "Gnu Cash", AppCenter does not provide the desired apps in the search results. The same is true if we just search for "Libre" or "Cash".

## Expected Behavior

Not sure how the current implementation looks like, but I expected the search to:

- Ignore whitespace in the Apps' name
- Allow to search for substrings in the App's name

## Environment

I'm on elementary 6 Daily.