GumGum: adds note that mediaType video is required for video products (#2551)
GumGum: adds note that mediaType video is required for video products (#2551)

* specifies us privacy is supported

* adds video support to gumgum md

* adds support for tcf 2

* adds new bid param to gumgum.md

* updates gumgum doc

* notes required mediaType for video products
prebid/prebid.github.io,prebid/prebid.github.io,prebid/prebid.github.io