support using a config file for the provider

[fawaf]

json or yaml format with the required details

e.g. infoblox.json

{
  "server": "<hostname>",
  "username": "nios_username",
  "password": "nios_password"
}

provider.tf

provider "infoblox" {
  config_file = "/home/blah/infoblox.json"
}