feat(kms): add keyring resource and datasource (#1049)

relates to STACKITTPR-410

docs/data-sources/kms_keyring.md

@@ -0,0 +1,38 @@
+---
+# generated by https://github.com/hashicorp/terraform-plugin-docs
+page_title: "stackit_kms_keyring Data Source - stackit"
+subcategory: ""
+description: |-
+  KMS Keyring datasource schema. Uses the default_region specified in the provider configuration as a fallback in case no region is defined on datasource level.
+---
+
+# stackit_kms_keyring (Data Source)
+
+KMS Keyring datasource schema. Uses the `default_region` specified in the provider configuration as a fallback in case no `region` is defined on datasource level.
+
+## Example Usage
+
+```terraform
+data "stackit_kms_keyring" "example" {
+  project_id = "xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx"
+  keyring_id = "xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx"
+}
+```
+
+<!-- schema generated by tfplugindocs -->
+## Schema
+
+### Required
+
+- `keyring_id` (String) An auto generated unique id which identifies the keyring.
+- `project_id` (String) STACKIT project ID to which the keyring is associated.
+
+### Optional
+
+- `region` (String) The resource region. If not defined, the provider region is used.
+
+### Read-Only
+
+- `description` (String) A user chosen description to distinguish multiple keyrings.
+- `display_name` (String) The display name to distinguish multiple keyrings.
+- `id` (String) Terraform's internal resource ID. It is structured as "`project_id`,`region`,`keyring_id`".