feat: expose inner client to interact w/ the API (#176)

Author: rhamzeh

src/main/java/dev/openfga/sdk/api/client/OpenFgaClient.java

@@ -54,6 +54,13 @@ public OpenFgaClient(ClientConfiguration configuration, ApiClient apiClient) thr
      * Utilities *
      *************/
 
+    /**
+     * Returns the underlying low-level OpenFgaApi instance.
+     */
+    public OpenFgaApi getApi() {
+        return api;
+    }
+
     public void setStoreId(String storeId) {
         configuration.storeId(storeId);
     }