[test] Use `next-data-api-endpoint` for Middleware HTTP method tests (#86157)
We use `https://next-data-api-endpoint.vercel.app` for most of our e2e test API calls. The `middleware-fetches-with-any-http-method` test suite was using `https://http-echo-kou029w.vercel.app`, which was soft-deleted recently, and that caused the tests to fail. Now we're using the `next-data-api-endpoint` for this test suite as well.