[Feature]: flatpak support

What is the installation method of your PatchMon server?

Docker

What is the version of your PatchMon server?

2.0.2

Briefly describe the feature

Add support to check on update status for flatpak installed packages, and apply as necessary.

Detailed description

My workstations use a combination of repos and flatpak for application install. While I can use patchmon to monitor and patch anything that comes via repo, I still have to manually update flatpak packages.

Why is this useful?

I'd love my flatpak apps to appear in the same reports as my out-of-date repo packages, and be able to drive their updates via the same inteface, further reducing the amount of manual CLI updates I need to run.