Support for `subnet_enforce_private_link_endpoint_network_policies` and `subnet_enforce_private_link_service_network_policies`

Support for subnet_enforce_private_link_endpoint_network_policies(type of map(bool) with key subnet name, value true or false) and subnet_enforce_private_link_service_network_policies(type of map(bool) with key subnet name, value true or false)

Add local variables to prevent unnecessary force replacement

1. Add local variables azurerm_subnets to prevent unnecessary force replacement
2. update README

Support Terraform 0.13 & Enhancement

1. Support Terraform 0.13
2. Add variable subnet_service_endpoints (type map(string)) to config the service_endpoints for each subnet

Update deprecated field `address_prefix`

Update deprecated field address_prefix. No influence for users.

Integration of terramodtest 0.5.0

1. Integration of terramodtest 0.5.0
2. Support Terraform 0.12
3. Support Azurerm 2.0
4. Remove the creation of resource group, import an existing resource group
5. address_space type use original list of string
6. Allow create vnet without nsg