Change custom actions and home dir

Upon creation of the rover home dir $HOME/.rover/ (checked each time rover starts), default files in pkg/rover/home will be copied into that new directory
Contents of pkg/rover/home is embedded into rover binary
Custom actions are now loaded from a yaml file actions.yaml from the rover home dir
Custom actions can request setupEnv: true in their definition which will call landingzone.SetupEnvironment()
landingzone.SetupEnvironment() is a new function which carries out all the account checking, identity checks, fully populates the Options struct, and sets all the environmental vars. It has been split off from prepareTerraformCAF which was getting too large

aztfmod / rovergo