Support threading arbitrary arguments through to IBuilder.

Currently, IBuilder only takes in the Location as an argument. I proposed adding a Context object of some kind that can be used to thread global (immutable!) state through to all builders. This would permit scenarios as follows:

let myBuilder = foo {
    doSomething // can access "name" set below with value "dave"
}

let template = arm {
    set_context "name" "dave"
}

Linked to #592 - this would allow us to globally turn on or off default switches such as default identity etc.

Thoughts @ninjarobot ?

[MoeJw]

I think this might be also handy when configuring Common things between resources like Diagnostic -setting and alerts etc. enable them for all resources we deploy instead of just creating one for every resource… but this might not be an easy thing to do

[TheRSP]

@isaacabraham I think this would be useful. We currently have env parameter which we pass through to all builders. One thing I don’t quite understand is how we would make use of the parameter. Would we need to copy the whole BuildResources method?