skaffold find-configs should error if a too-new config file is found

I tried to launch the `examples/helm-deployment` within CC-VSC, which failed in a surprising way. In diagnosing the issue, it turns out that I was actually in `integration/examples/helm-deployment` and the `skaffold.yaml` had too new of an apiVersion. CC uses `skaffold find-configs` to find the configuration files, which in this case returns nothing:
```
$ skaffold version
v1.20.0
$ skaffold find-configs --output json
{}
```

As a result, CC-VSC then tried to do a `skaffold init --analyze`, which failed (due to Helm).

### Expected behavior

`skaffold find-configs` should probably report all `skaffold.yaml` regardless of the apiVersion. It's possible a user is running an older version of Skaffold. Let the version error come up when they attempt to launch.

### Information

- Skaffold version: 1.20.0
- Operating system: macos
- Installed via: Google Cloud SDK
- Contents of skaffold.yaml:
http://github.com/GoogleContainerTools/skaffold/blob/master/integration/examples/helm-deployment/skaffold.yaml