Enable building in Linux from default checkout

[penguin359]

This is the third in a series of PRs to clean up the build of Walnut-Chat Headless on Linux.

This PR ensures some auto-generated files from premake5 are ignored by Git and enables premake5 to be executable from the initial checkout of Walnut.

I have this PR as a draft for the moment as it depends on the following PRs to be complete:

StudioCherno/Walnut-Networking#2 TheCherno/yaml-cpp#4

Once those have been approved, I'd like to update this PR to point to the updated commits before this is merged.