Use internal app gw listener for work plane vault endpoint

[ripa1993]

In cloud init definition for worker plane

module "cloud_init_worker_plane" {
  source          = "git::ssh://git@github.com/bitrockteam/caravan-cloudinit"
  ...
  vault_endpoint  = "http://${azurerm_linux_virtual_machine.control_plane[0].private_ip_address}:8200"
}

We are using a single instance as vault endpoint, we can leverage the internal ip of the app gateway as a way to provide HA for internal vault comms