Create fr_fr.json

Early start to the french translation. We could maybe add incomplete or missing translation requests there? I started a crowdin project and would be happy to to give the managger role on it to the mod author/manager. We could maybe add incomplete or missing translation requests there? https://crowdin.com/project/minecraft-tetra-mod/ Even if manged by me, I'm translating the mod in French rn and will upload it on here when done