Streaming: Remove usage of Observable in favor of fetch

```js
while (!ended && retries > 0) {
  try {
    await fetch(...);
  } catch (err) {
    console.warn('failed to refresh token');
    retries--;
    // do some sleep to prevent spamming the server
    return;
  }

  retries = DEFAULT_RETRIES;
  // sleep for refreshTokenInterval
}
```