Add games/rbdoom3bfg-vk

Hello! This is a port of the game DOOM-3-BFG to OpenBSD. This is the open source code of .RBDOOM-3-BFG. Vulkan version. [send to ports@ 2025-30-05](https://marc.info/?l=openbsd-ports&m=174860101518720) Tested on amd64 architecture on OpenBSD 7. 7 installed on real hardware: ASUS TUF GAMING B450M-PRO II AMD Ryzen 5 5600G AMD Radeon RX 580 PowerColor. (amdgpu) Works as good as on Linux. Video: https://www.youtube.com/watch?v=7E5OFp_dHfA https://www.youtube.com/watch?v=a0zuUrsbXCY I want to add this to the official ports tree, so please leave any feedback or suggestions on how to improve it. Thanks! Source on Github: https://github.com/RobertBeckebans/RBDOOM-3-BFG