feat: implement stackit git instances (#791)

* feat: implement stackit git instances

* review changes

docs/data-sources/git.md

@@ -0,0 +1,38 @@
+---
+# generated by https://github.com/hashicorp/terraform-plugin-docs
+page_title: "stackit_git Data Source - stackit"
+subcategory: ""
+description: |-
+  Git Instance datasource schema.
+  ~> 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_git (Data Source)
+
+Git Instance datasource schema.
+
+~> 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_git" "git" {
+  project_id  = "xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx"
+  instance_id = "xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx"
+}
+```
+
+<!-- schema generated by tfplugindocs -->
+## Schema
+
+### Required
+
+- `instance_id` (String) ID linked to the git instance.
+- `project_id` (String) STACKIT project ID to which the git instance is associated.
+
+### Read-Only
+
+- `id` (String) Terraform's internal resource ID, structured as "`project_id`,`instance_id`".
+- `name` (String) Unique name linked to the git instance.
+- `url` (String) Url linked to the git instance.
+- `version` (String) Version linked to the git instance.