Handle special case for Slack User Group in search

- Adjust Slack User Group channel search pending migration
- Add TODO to remove hack after migration to new system

graphql2/graphqlapp/destinationtypes.go

@@ -195,6 +195,14 @@ func (q *Query) DestinationFieldSearch(ctx context.Context, input graphql2.Desti
 		opts.Search = *input.Search
 	}
 
+	if input.DestType == destSlackUG && input.FieldID == slack.FieldSlackChannelID {
+		// Hack: Slack User Group channel search is a special case, until
+		// it is migrated to the new search system.
+		//
+		// TODO: remove this when slack user group is moved to the nfydest.Registry.
+		input.DestType = slack.DestTypeSlackChannel
+	}
+
 	res, err := q.DestReg.SearchField(ctx, input.DestType, input.FieldID, opts)
 	if err != nil {
 		return nil, err