chore(pagination): add double truncation example

This adds a double truncation example which is required to close gitlab-org/gitlab-services/design.gitlab.com#422 (closed) where we'll add missing demos in https://design.gitlab.com/components/pagination#pagination

Desktop	Mobile

Once this is merged, we'll be able to update the component's page as follows:

NOTE: we'll remove mobile-specific examples because we can simply resize the window while viewing the demos to switch between desktop and mobile viewports