Update workspace notification settings

Updates one or more durable notification-policy sections. Enabling auto top-up requires an existing saved payment method identifier and verified two-factor authentication. An existing auto top-up configuration may be updated without repeating the MFA acknowledgement. To enable auto top-up without MFA, clients must explicitly set mfa_bypass_acknowledged to true and provide the exact mfa_bypass_phrase value I ACCEPT THE RISK; payment collection remains an interactive account flow.