feat: Convert all app files to JS

packages/backend/src/apps/slack/common/get-current-user.js

@@ -0,0 +1,11 @@
+const getCurrentUser = async ($) => {
+  const params = {
+    user: $.auth.data.userId,
+  };
+  const response = await $.http.get('/users.info', { params });
+  const currentUser = response.data.user;
+
+  return currentUser;
+};
+
+export default getCurrentUser;