New Resource: azurerm_disk_pool

[tombuildsstuff]

This PR introduces a new resource azurerm_disk_pool which supersedes the existing azurerm_storage_disks_pool - this is because the existing resource is unrelated to the Storage package and is a collection of (Managed) Disks. Since there's a number of Disk related resources (and will be more with #14268) - this pulls the existing resource and this new resource out into it's own package.

There's a follow up here to move Managed Disks into this package too, but that's outside the scope of this PR.

Dependent on #14673 and #14672

[lonegunmanb]

Hello @tombuildsstuff , should I continue my work #14268 based on this pr once it has been merged? It's your call, awaiting for your instruction.

[tombuildsstuff]

Sku needs to be ForceNew in both of these:

------- Stdout: -------
=== RUN   TestAccDiskPool_upgradeSku
=== PAUSE TestAccDiskPool_upgradeSku
=== CONT  TestAccDiskPool_upgradeSku
=== CONT  TestAccDiskPool_upgradeSku
testcase.go:110: Step 3/4 error: After applying this test step, the plan was not empty.
stdout:
Terraform used the selected providers to generate the following execution
plan. Resource actions are indicated with the following symbols:
~ update in-place
Terraform will perform the following actions:
# azurerm_disk_pool.test will be updated in-place
~ resource "azurerm_disk_pool" "test" {
id                  = "/subscriptions/*******/resourceGroups/acctestRG-diskspool-211223144533983359/providers/Microsoft.StoragePool/diskPools/acctest-diskspool-w1thg"
name                = "acctest-diskspool-w1thg"
~ sku_name            = "Standard_S1" -> "Premium_P1"
tags                = {}
# (4 unchanged attributes hidden)
}
Plan: 0 to add, 1 to change, 0 to destroy.
--- FAIL: TestAccDiskPool_upgradeSku (1086.98s)

[katbyte]

Thanks @tombuildsstuff - LGTM 🏗️

[tombuildsstuff]

Tests pass:

[github-actions]

This functionality has been released in v2.91.0 of the Terraform Provider. Please see the Terraform documentation on provider versioning or reach out if you need any assistance upgrading.

For further feature requests or bug reports with this functionality, please create a new GitHub issue following the template. Thank you!

[github-actions]

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