Return OCTClientErrorUnsupportedServerScheme when a 301 redirect results in a 403

Attempting to log in to an SSL-enabled Enterprise server with an HTTP URL automatically redirects the client but strips the `Authentication` header, resulting in a `403`.

This adds an `OCTClientErrorUnsupportedServerScheme` error and exposes `OCTServerSecureEnterpriseScheme` so a client can try again.