Added 3 default subnet_prefixes to the subnet list in variables.tf m…

[diogomaul]

Fixes #1

Changes proposed in the pull request:

I've added 3 default subnet_prefixes to the list in variables.tf so that it matches the 3 default subnet_names. This will help people to run/test the code without adding any optional variables, especially people that are just starting to learn Terraform modules.

Without this fix, Terraform Plan throws the following error when you run it without adding subnet_prefixes (or names):
Error: Invalid index
│
│ on .terraform/modules/vnet/main.tf line 20, in resource "azurerm_subnet" "subnet":
│ 20: address_prefixes = [var.subnet_prefixes[count.index]]
│ ├────────────────
│ │ count.index is 1
│ │ var.subnet_prefixes is list of string with 1 element
│
│ The given key does not identify an element in this collection value: the
│ given index is greater than or equal to the length of the collection.
╵
╷
│ Error: Invalid index
│
│ on .terraform/modules/vnet/main.tf line 20, in resource "azurerm_subnet" "subnet":
│ 20: address_prefixes = [var.subnet_prefixes[count.index]]
│ ├────────────────
│ │ count.index is 2
│ │ var.subnet_prefixes is list of string with 1 element
│
│ The given key does not identify an element in this collection value.

[github-actions]

MAIN BRANCH PUSH DETECTED DUE TO #71, THIS PR NEED TO BE UPDATED TO TRIGGER CI.

[github-actions]

MAIN BRANCH PUSH DETECTED DUE TO #72, THIS PR NEED TO BE UPDATED TO TRIGGER CI.

[github-actions]

MAIN BRANCH PUSH DETECTED DUE TO #, THIS PR NEED TO BE UPDATED TO TRIGGER CI.

[lonegunmanb]

Thanks @diogomaul for opening this pr and apology for this late reply. We've changed a lot of files to add a CI pipeline to this module so I just re-write this pr as #73. Again, thanks for your contribution and understanding, I'm closing this pr now.