Upgrade terraform and provider versions

[reifnir]

• When creating multiple objects, such as the DNS verification TXT records, switched from count to for_each. Using count can be buggy when items in a list are changed. If you're creating objects and their state index changes, Terraform will try to update both at once or remove/add at the same time leading to conflicts where you have to retry a number of times. Using for_each instead gives more stable state names. Ex: module.custom_dns_static_site.azurerm_app_service_custom_hostname_binding.static_site["www"] instead of module.custom_dns_static_site.azurerm_app_service_custom_hostname_binding.static_site[0].
• Marked the module compatible with versions beyond 0.14.
• Bumped the ACME provider used to generate Let's Encrypt certs from 2.4.0 to the current version, 2.9.0.
• Now using azurerm Terraform provider version 3 and later.
• Moved away from deprecated objects azurerm_function_app and azurerm_app_service_plan resource for the newer azurerm_linux_function_app and azurerm_service_plan.
  • Unfortunately, there are still a couple of bugs in azurerm_linux_function_app in that some properties (custom_domain_verification_id, default_hostname) are not yet implemented. There are already a couple of MRs that are just awaiting responses from Hashicorp.
    • terraform-provider-azurerm/issues/16263
    • terraform-provider-azurerm/issues/17444
  • In order to use the newer resources, I needed to add a deprecated azurerm_function_app data reference as a workaround. This will be removed as soon as the missing functionality is released.