Add outlet element to the templated combos in the Grid Cascading Combos sample

[ddaribo]

Description

Related to #3499

The Grid with Cascading Combos sample, when implemented with more records would involve scrolling. As the combos are reused because of virtualization, on scroll any prior opened dropdown would remain open. Adding an outlet element to the combos is needed so that the built-in logic in the IgxGrid that closes any overlays on scroll could handle this scenario.

<igx-simple-combo .." [overlaySettings]="{ outlet: grid1.outlet }">