Allow configuration of litedb root path

I'm brand new to Litestack, I've just been playing with Rails + sqlite in production manually (setting the journal mode to WAL).

It would be nice if we could configure the Litesupport root outside of using an env variable so that I don't have to add yet another env variable to production, and it works the same as dev/staging.

What about using a Rails config initializer? If you are open to this idea, let's hash it out and then I'll create a PR for it.