Add a contact with its consent basis

Add one contact. A subscribed contact (the default) requires consent_basis: how this person agreed to receive your email. Use status: "unsubscribed" to record an opt-out. Addresses already suppressed or unsubscribed from the workspace are stored with that status, never as subscribed. Optional tags (up to 50, each up to 60 characters) are attached to the new contact. Returns 409 when the email already exists.