Option to filter "installed" apps which were installed via Play Store

[keithfancher]

Is your feature request related to a problem? Please describe.
There's currently no way to distinguish which apps in the "installed" tab are actually installed via F-Droid/Droidify and which were installed via the Play Store. (Other than clicking into each individual app, scrolling down to the versions, and tapping the latest version to see the error message about signatures not matching.)

I think there are many cases where this would be useful. But especially for new users!

As a user who recently started using F-Droid (and Droidify), I installed one or two apps, but then was surprised to see quite a large list of apps in my "installed" tab. Every F-Droid-available app shows in this list, even if installed via Play. While I'm in the progress of slowly "migrating" my apps (i.e. uninstalling and then re-installing with Droidify), I've needed to manually keep a checklist as I go. And if I want to confirm, I have to do the above steps: manually go into each individual app and tap a version.

Describe the solution you'd like
Droidify can have an option, either in the settings or a one-off toggle in the "installed" screen itself, to filter out these apps. It can just broadly be any app whose signature doesn't match, probably -- doesn't have to get fancy with installation source or anything.

Alternatively, instead of filtering, a visual indication of some kind in the list would be plenty! Just some way to know which apps don't have matching sigs, if any.

Describe alternatives you've considered
The only alternatives I can think of are:

1. To just all-out uninstall everything and then re-install everything all at once (which is not feasible for most users, especially since configuration is usually deleted when an app is uninstalled) or
2. ...making a checklist and tracking apps manually.

And even this doesn't account for users who must, for whatever reason, keep an F-Droid-available app installed via Play Store for some reason. (If the Play Store version has a feature they need, e.g.)

Additional context
Droidify is great! Thanks for all your hard work 😄