[2023] Make undead leagacy an official DLC

It probably couldn't happen anyway because the author used a hacking mod system instead of one of the supported mod systems to inject the mod code into the client. Not to mention that it's buggy as hell.

They should have used Harmony for it instead of BepInEx. The latter is for games that don't support modding natively. 7 Days has full modding support with existing developed platforms. It probably wouldn't cause as many issues with the client if they had done it properly.