Fix notices on manage premiums page

Fix notices on manage premiums page

This addresses notices at
https://dmaster.localhost:32353/civicrm/admin/contribute/managePremiums?reset=1

These are probably also addressed by the admin ui / sk conversion but note that this also
covers the tab on the contribution page

Note that combined with https://github.com/civicrm/civicrm-core/pull/28238
this fixes most of the issues I encountered trying to configure a premimum
but there are still a bunch of notices when I attempt to use one.

Also, having switched to using apiv4 I have added some tpl escaping