feat(mailerlite): add mailerlite integration

packages/backend/src/apps/mailerlite/auth/verify-credentials.js

@@ -0,0 +1,10 @@
+const verifyCredentials = async ($) => {
+  await $.http.get('/campaigns');
+
+  await $.auth.set({
+    screenName: $.auth.data.screenName,
+    apiKey: $.auth.data.apiKey,
+  });
+};
+
+export default verifyCredentials;