Since we now call `loadConfig()` in various processes our `execOnce`
handling isn't tracking when we have already shown warnings/logs in
another process so this adds a `silent` flag that we can leverage when
calling `loadConfig()`.
## Bug
- [x] Related issues linked using `fixes #number`
- [x] Integration tests added
- [ ] Errors have a helpful link attached, see
[`contributing.md`](https://github.com/vercel/next.js/blob/canary/contributing.md)
Fixes: [slack
thread](https://vercel.slack.com/archives/C03KAR5DCKC/p1674351677627259)
440560fbbb