Archives an existing, currently non-archived contact for the
authenticated client.

Requires contact_id. Only affects contacts where
contact_archived_at IS NULL - attempting to archive an
already-archived contact returns a failure response.

On success:

• contact_important, contact_billing, and contact_technical are
  reset to 0.
• contact_archived_at is set to the current timestamp.
• If the contact has an associated user (contact_user_id > 0),
  that user record is also archived (user_archived_at set to
  the current timestamp).