collie kit apply should include platform.hcl with expose = true

[JohannesRudolph]

When collie generates a new terragrunt configuration for invoking a kit module via collie kit apply
it generates an include block like

include "platform" {
  path   = find_in_parent_folders("platform.hcl")
}

Using platform variables like e.g. AAD Tenant Id is very common and the missing expose = true trips up the workflow for engineers new to terra grunt.

[JohannesRudolph]

Fxied in #270