Runtime configuration for SwaggerUI plug

[D4no0]

This PR is related to #492

You are able now to define configs in the following way:

defmodule RuntimeConfig do
  def on_complete do
    "function() { ui.preauthorizeApiKey("bearer", "your generated token here"); }"
  end
end

scope "/" do
  pipe_through :browser # Use the default browser stack
  get "/swaggerui", OpenApiSpex.Plug.SwaggerUI,
    path: "/api/openapi",
    on_complete: {RuntimeConfig, :on_complete}
end

The configuration is evaluated each time the call/2 function from the plug is invoked.

[zorbash]

Please escape double quotes or use the ~S sigil.

[zorbash]

The SwaggerUI module is a Plug, it can be used even by a non-phoenix app specifying its routes in a router.ex.

[D4no0]

Ah my bad, I will update the documentation.