Verify the Bruno Flatpak on Flathub

[AligningEntropy]

I have checked the following:

• [X] I've searched existing issues and found nothing related to my issue.

Describe the feature you want to add

Flatpak support was enabled in #623 and has (at the time of writing this) around 11,000 installs; however, the Flatpak currently is marked as unverified.

This is problematic as some Linux distributions, such as Mint, are starting to hide unverified flatpaks by default (making them not show up in search) for security reasons and many users can be scared off from downloading something with these intimidating warning banners.

Per Flathub's documentation, the fix for this requires @helloanoop to "verify" themselves by linking their Flatpak account to this repo / the usebruno website. The steps listed appear pretty straight forward, so hopefully this won't take much effort.

Mockups or Images of the feature