Restore azurerm_nginx_configuration resource and data source

[puneetsarna]

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.

[puneetsarna]

@wuxu92 We'd like to restore this functionality for the reasons called out in the PR description. Until we have an internal discussion between us, Microsoft, and Terraform folks, can we please restore this functionality? Thanks!!

[puneetsarna]

Cross posting these from where the functionality was deprecated:

#24276 (comment)

#24276 (comment)

[puneetsarna]

Based on chats with @wuxu92, the below is a public facing example of a use-case for NGINXaaS that breaks if we retire the azurerm_nginx_configuration resource:

1. The user first creates azurerm_nginx_deployment.
2. The user proceeds to create the azurerm_nginx_certificate to add certificates to their deplyoment.
3. The user proceeds to create the azurerm_nginx_configuration referencing the certificate via file paths (and the added depends_on to ensure sequence of operations) to secure their deployment.

This is a very common use-case for our service and will break if we retire the configuration resource.

https://github.com/nginxinc/nginxaas-for-azure-snippets/blob/main/terraform/certificates/main.tf has these resources in action. Right now, I can create these resources in a single terraform run but if we embed the configuration inside the deployment, the user workflow breaks.

I hope the above helps explain why this PR has been staged.

[agazeley]

LGTM! 👍

[puneetsarna]

• Need to deprecate the new embedded fields.
• Add a test for certs and configs being used together to establish a workflow contract.

[puneetsarna]

#25740 superseded this PR. closing it in favor of #25740.

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