Added Lua global variable example

[RobinsAviary]

Heyo! This is just a basic example to show people how to expose a basic global variable and create a basic state in lua. I think I might also create a simpler "Hello Lua" example as well, but I wanted to start with this PR. Let me know what you think. Thanks!

Checklist before submitting:

• This example has been added to .github/workflows/check.yml (for automatic testing)
• This example compiles cleanly with flags -vet -strict-style -vet-tabs -disallow-do -warnings-as-errors
• This example the naming and style convention: https://github.com/odin-lang/examples/wiki/Naming-and-style-convention (exceptions can be made for ports of examples that need to match 1:1 to the original source).
• By submitting, I understand that this example is made available under these licenses: Public Domain and Odin's BSD-3 license. Only for third-party dependencies are other licenses allowed.

[karl-zylinski]

Thanks!