feat(provider): add repository actions variable resource

Closes #8

docs/resources/repository_actions_variable.md

@@ -0,0 +1,32 @@
+---
+# generated by https://github.com/hashicorp/terraform-plugin-docs
+page_title: "forgejo_repository_actions_variable Resource - terraform-provider-forgejo"
+subcategory: ""
+description: |-
+  Use this resource to create and manage a repository actions variable.
+---
+
+# forgejo_repository_actions_variable (Resource)
+
+Use this resource to create and manage a repository actions variable.
+
+## Example Usage
+
+```terraform
+resource "forgejo_repository_actions_variable" {
+  data       = "value"
+  name       = "test"
+  owner      = "adyxax"
+  repository = "example"
+}
+```
+
+<!-- schema generated by tfplugindocs -->
+## Schema
+
+### Required
+
+- `data` (String) The variable's data.
+- `name` (String) The variable's name. It must be uppercase or the plan will not be idempotent.
+- `owner` (String) The variable's owner.
+- `repository` (String) The variable's repository.