docs: oas (#197)

Adds OpenAPI specification of Storefront and Admin APIs.
Updates docs project.

docs-util/helpers/use-api.js

@@ -0,0 +1,21 @@
+const axios = require("axios").default;
+
+const ServerTestUtil = {
+  port_: null,
+  client_: null,
+
+  setPort: function (port) {
+    this.client_ = axios.create({ baseURL: `http://localhost:${port}` });
+  },
+};
+
+const instance = ServerTestUtil;
+
+module.exports = {
+  setPort: function (port) {
+    instance.setPort(port);
+  },
+  useApi: function () {
+    return instance.client_;
+  },
+};