teleport cache & tctl requests approve issue 

While testing https://github.com/gravitational/teleport-plugins @marshall-lee has ran into issues approving workflow requests using `tctl requests approve`. 

It was only possible to get this working by turning off the Teleport Cache, which isn't currently documented. 

```
teleport:
  cache:
    enabled: false
```

Teleport:  v4.2.0-rc.3
OS:           Running on MacOS 