auth customisation options for use outside of Azalea

[1zun4]

I am currently looking forward to using azalea-auth for https://github.com/CCBlueX/LiquidLauncher to replace the horrible "miners" library, which has no proper error handling and keeps throwing error codes that a normal user cannot really interpret.

But there is one big problem, and that is that I cannot use my own client ID without forking this repository, and I do not want to use the Nintendo Switch client ID. Also, the fact that you cannot pass your own cache to auth, only a path to an existing cache file, is another thing that would require me to fork it.

Since azalea is more of a library, it makes sense to give the programmer using the library more control without having to fork the repository and change the code.