Add /v1/actions API call to HetznerApi client

This will allow the polling of asynchronous actions from the Hetzner API
without consuming the main rate limit of the other (main) endpoints.

Author: daniel-gray-jemmic

src/main/java/cloud/dnation/hetznerclient/HetznerApi.java

@@ -30,6 +30,17 @@
  * For full version, check <a href="https://docs.hetzner.cloud/">official documentation</a>
  */
 public interface HetznerApi {
+
+    /**
+     * Poll the status of an asynchronous API on the Hetzner Cloud.
+     * <p>Normally, the rate limit of this API is higher and separate from the other API calls,
+     * as it is preferred to poll the /actions endpoint to wait for asynchronous action to complete.</p>
+     * @param actionId the ID of the action whose status you want to poll
+     * @return the full Action object, including its current status
+     */
+    @GET("/v1/actions/{id}")
+    Call<ActionResponse> pollAction(@Path("id") Long actionId);
+
     /**
      * Get all images that matches given label expression.
      *