web: clear out selecteds list after an API event to ensure a fresh copy of the policies-to-delete list (#8125)

* web: clear out selecteds list after an API event to ensure a fresh copy of the policies-to-delete list

* Prettier had opinions.

* web: A better fix

This fix creates a new property of Table, 'clearOnRefresh', which
automatically empties the `selectedElements` list when an EVENT_REFRESH
event completes.  Set this flag on any table that uses the
`selectedElements` list for bulk deletion; this ensures that stale
data in the `selectedElements` list will not persist and interfere
with future deletion events.

web/src/admin/events/RuleListPage.ts

@@ -27,6 +27,7 @@ import {
 export class RuleListPage extends TablePage<NotificationRule> {
     expandable = true;
     checkbox = true;
+    clearOnRefresh = true;
 
     searchEnabled(): boolean {
         return true;