feat(popover): Allow forcing of direction for popover

The default behavior of the popover is to override and reverse the direction if the height of the popover causes it to run off the edge of the viewport.  

This should be allowed to be overridden in cases where the popover should always flow in one direction based on the specs of the UI.

[[#80100378](https://www.pivotaltracker.com/story/show/80100378)]