This fix means a behaviour change to GET calls. Instead of a JSON
payload, instead a filter param has been added to the URL itself. GET
payloads are very unexpected in API designs, even though supported.
* Todo write tests (with postman?)
* Turn isAdmin logic into common middleware
```bash
curl "http://localhost:3002/v1/schedules?apiKey=...&userId=2"
```
```bash
curl "http://localhost:3002/v1/schedules?apiKey=..." \
-d '{"name":"Hello", "userId": 2}' \
-H 'Content-Type: application/json'
```
Alex van Andel