Add support for named config overrides in Fides.js

[Catherine Smith]

          This is specifically what some applications need to support -  a global object on `window` that they can prefill with some options for various other JS to pull from. It can't be namespaced just to Fides as it's shared with other tools.

It'd be good to support an explicit config option for init that names this though, like

Fides.init(extra: window.config.fides)
// or
Fides.init(extra: window.options)
// or
Fides.init(extra: window.my.special.options

?

Originally posted by @NevilleS in #4297 (comment)