api-types: api: datatore: add notification-mode parameter

api-types: api: datatore: add notification-mode parameter

This one lets the user choose between the old notification behavior
(selecting an email address/user and always/error/never behavior per
datastore) and the new one (emit notification events to the
notification system)

Signed-off-by: Lukas Wagner <l.wagner@proxmox.com>
Tested-by: Gabriel Goller <g.goller@proxmox.com>
Reviewed-by: Gabriel Goller <g.goller@proxmox.com>
Tested-by: Maximiliano Sandoval <m.sandoval@proxmox.com>
Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>