Support video content in Layout.ArticleStack
Support video content in Layout.ArticleStack

Previously one could only specify on type of card in the article stack.
Now we want to be able to support both text and video content in
the template A and B apps so we need to specify a slot for video
cards as well.

https://phabricator.endlessm.com/T14516

endlessm/eos-knowledge-lib,endlessm/eos-knowledge-lib,endlessm/eos-knowledge-lib,endlessm/eos-knowledge-lib