Add Example for using config json file downloaded from install.nutanix.com to image nodes using terraform nutanix foundation

[bhati-pradeep]

Is your feature request related to a problem? Please describe.
Instead of mentioning all the details like cvm_ip, ipmi_ip, etc. manually, we can leverage the config.json file downloaded from install.nutanix.com to create the spec dynamically.

Example :
We can create local variable to get details from config using -
locals{ config = (jsondecode(file("config.json"))) }