Add Flatpak installation

[mmohaveri]

Is your feature request related to a problem? Please describe. I use flatpak to manage my applications on my Debian machine, but Kreya does not provide any flatpak.

Describe the solution you'd like Add support for the flatpak,. As Kreya already supports snap, I don't think it takes too much effort to add flatpak support as well.

[latonz]

Thanks for your request, we added support for flatpak to our roadmap. However, we cannot provide a release version or date yet.

[HyperAlch]

I literally can not use Kreya as a NixOS user because of the lack of Flatpak support.

Why would you focus on snap, a format no one wants or uses other than Ubuntu, instead of Flatpak.

Your screwing over the Linux community super hard.