feat: Onboard IaaS Public IP range datasource (#633)

* Add "stackit_public_ip_range" datasource
  * Add docs and example

docs/data-sources/public_ip_ranges.md

@@ -0,0 +1,35 @@
+---
+# generated by https://github.com/hashicorp/terraform-plugin-docs
+page_title: "stackit_public_ip_ranges Data Source - stackit"
+subcategory: ""
+description: |-
+  A list of all public IP ranges that STACKIT uses.
+  ~> This resource is in beta and may be subject to breaking changes in the future. Use with caution. See our guide https://registry.terraform.io/providers/stackitcloud/stackit/latest/docs/guides/opting_into_beta_resources for how to opt-in to use beta resources.
+---
+
+# stackit_public_ip_ranges (Data Source)
+
+A list of all public IP ranges that STACKIT uses.
+
+~> This resource is in beta and may be subject to breaking changes in the future. Use with caution. See our [guide](https://registry.terraform.io/providers/stackitcloud/stackit/latest/docs/guides/opting_into_beta_resources) for how to opt-in to use beta resources.
+
+## Example Usage
+
+```terraform
+data "stackit_public_ip_ranges" "example" {}
+```
+
+<!-- schema generated by tfplugindocs -->
+## Schema
+
+### Read-Only
+
+- `id` (String) Terraform's internal resource ID. It takes the values of "`public_ip_ranges.*.cidr`".
+- `public_ip_ranges` (Attributes List) A list of all public IP ranges. (see [below for nested schema](#nestedatt--public_ip_ranges))
+
+<a id="nestedatt--public_ip_ranges"></a>
+### Nested Schema for `public_ip_ranges`
+
+Read-Only:
+
+- `cidr` (String) Classless Inter-Domain Routing (CIDR)