[Request] Submit Mesen-X to Flathub

[vermadas]

If Mesen-X was available on Flathub, it could be easily installed on the Steam Deck. This would allow the use of Mesen without the need to use RetroArch.

https://github.com/flathub/flathub/wiki/App-Submission

I have not verified that the code meets the requirements for app submission.

Thanks!