Adding numary to nixos package directory

[pcasaretto]

I'm trying to learn and use Nix, so to test that and numary at the same time I've proposed adding numary to the Nixos package directory.

https://github.com/NixOS/nixpkgs/pull/191106

I've followed the instructions for building present at the current Dockerfile but I could use some help with the tests.

[jdupas22]

Hey @pcasaretto ! Thanks a lot for your contribution ! We'd love to help you on this ! We can chat about it on our public slack if you want, you can join us here : https://www.formance.com/slack you'll find a brand new channel where we can easily get in touch =)