Restore azurerm_nginx_configuration resource and data source

[valyria257]

Reverts #24276

There are a couple of things here:

• The default configuration/import error issue was resolved. See changelog from March 13, 2024
• This is a breaking change from a product use-case perspective as it breaks our HTTPS use-case where in the workflow is:
  1. Create deployment.
  2. Create certificate.
  3. Create configuration.

With configuration now being inline, the use workflow breaks as 1 and 3 cannot be separated.

• certificates should also not be inline since different roles may mange deployments, certificates, and configurations separately

To fix this, the change to remove the azurerm_nginx_configuration is reverted, and the field that was added to replace it is deprecated.

[puneetsarna]

is this how features are deprecated in TF? I have not looked at this function but I vaguely remember that this was for breaking changes when the provider gets a 4.0 bumped.

[valyria257]

Good question! I got that from this contributing guide: https://github.com/hashicorp/terraform-provider-azurerm/blob/main/contributing/topics/guide-new-fields-to-resource.md#renaming-and-deprecating-a-property, but could use some direction here if there's a different way.