Raise ClientError when we get a redirect from harvest

We want to raise a ClientError (rather than a parsing exception) from the Harvest gem when we get this message:
```
<html><body>You are being <a href=\"https://api.harvestapp.com/company/inactive\">redirected</a>.</body></html>
```

This way we know when we get this specific error in FundingGates and can disconnect the harvest token whenever harvest sends us this response.