Add max-height to CustomSelectControl menu

[Aljullu]

In WooCommerce Blocks we used the CustomSelectControl component to create a Country selector (see woocommerce/woocommerce-blocks#1585).

It had the issue that when all countries were displayed, the dropdown was taking the height of the entire screen. It could be easily fixed adding a max-height property to the menu, but probably we might want to do this upstream so all consumers of CustomSelectControl get this default max-height.