feat: improve on user_data

[Evans Thiringai Njoroge]

Currently i tried using user_data via terragrunt and it's unable to recognize direct user_data, base64 encoded user_data and also file based user_data...
I would suggest changing the user_data variable to ...

variable "user_data" {
type = string
description = "The user data script"
}

This way one can add user_data directly or refer to filebase64("/path_to_file")