Added support for the list of private_ips

[antonbabenko]

Fixes #102

[dermyrddin]

But it seem to break single node creation without specifying private_ip:

Error: Error in function call

  on .terraform/modules/mongo_1/terraform-aws-modules-terraform-aws-ec2-instance-f03dffe/main.tf line 27, in resource "aws_instance" "this":
  27:   private_ip = element(
  28:
  29:
  30:
    |----------------
    | count.index is 0
    | var.private_ip is ""
    | var.private_ips is empty list of string

Call to function "element" failed: cannot use element function with an empty
list.

[antonbabenko]

My bad, I was too fast, fixed in bc0a43c which is part of v2.3.0.

[github-actions]

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