Add configuration value for what auto-require adds

[NyakoFox]

Auto-require always adds the require function specifically. However, it's common in projects to have their own special require functions, like import or include -- so this PR adds a configuration option which lets you change what it imports.

Lua.completion.requireFunction defaults to "require". I think I did this right?

This is open as a draft because I'm unable to test this -- I don't fully understand the environment or how to debug this project. If someone could test this, it'd be great. (The built exe did nothing when ran, unlike the exe included in VSCode... not really sure what's happening there.)