GetSecret doesn't return any data

[razzeee]

It seems to me like

https://github.com/lvermeulen/Keycloak.Net/blob/main/src/Keycloak.Net/Clients/KeycloakClient.cs#L88

shouldn't be Credential but Credentials from the User scope. That at least would match up with the return I get from the api manually.

I think GenerateSecret might be broken due to that too.