Add support for creation_option "Restore" on managed disks (issue #3421)

[sean-nixon]

First time contributing and go rookie so I'm open to feedback and let me know if I'm violating any guidelines.

Took a stab at issue #3421. The documentation doesn't really document the Restore option other than that it is a valid value for createOption. Based on this issue and my own experience in our Azure environment, however, this gets set when a disk is restored from backup or created during failover in Azure Site Recovery. Along with it, the sourceResourceId gets set.

For reference, below is some sanitized output from the Azure CLI of a disk created during Site Recovery failover (Azure to Azure):

az disk show -g rg -n disk --query creationData
{
  "createOption": "Restore",
  "imageReference": null,
  "sourceResourceId": "/subscriptions/xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx/resourceGroups/rg/providers/Microsoft.Compute/disks/disk-ASRReplica/bookmark/16db43c8-f886-48df-934a-3437e5f4f75c",
  "sourceUri": null,
  "storageAccountId": null
}

Acceptance tests are difficult for this one. I'm not sure if it is actually possible to create a disk using the "Restore" option using the normal disk API since I cannot find IDs in that format anywhere within Azure and it is not documented in the API docs (https://docs.microsoft.com/de-de/azure/templates/microsoft.compute/2018-09-30/disks#creationdata-object).

Fixes #3421

[tombuildsstuff]

LGTM - thanks for this @sean-nixon

[tombuildsstuff]

@sean-nixon thanks for this PR - as you've mentioned acceptance tests are difficult for this one, since this is just adding another value to the validation I think we should be good without these here (since we can see the CLI returns them) 👍

[ghost]

This has been released in version 1.30.0 of the provider. Please see the Terraform documentation on provider versioning or reach out if you need any assistance upgrading. As an example:

provider "azurerm" {
	version = "~> 1.30.0"
}
# ... other configuration ...

[ghost]

I'm going to lock this issue because it has been closed for 30 days ⏳. This helps our maintainers find and focus on the active issues.

If you feel this issue should be reopened, we encourage creating a new issue linking back to this one for added context. If you feel I made an error 🤖 🙉 , please reach out to my human friends 👉 hashibot-feedback@hashicorp.com. Thanks!