[Discover] Single doc view exit UI

[nickofthyme]

Describe the feature:

In the discover expanded document flyout, we have an option to view as Single document. Clicking this directs you to a full screen view of the Table/Json view of the current document.

Once on the Single document page there is no button or keyboard shortcut (i.e. escape) to bring to back to discover, apart from the breadcrumb and browser back, both of which would clear the discover state.

https://user-images.githubusercontent.com/19007109/219506872-872398ba-70c0-4537-a1ba-c3b911f4298e.mp4

Comparing this to the full screen mode of the main Document table, which has both an exit UI and keyboard return shortcut.

Describe a specific use case for the feature:

I don't like UX that traps users into a given state with no easy way out, this is also likely poor A11y.

[elasticmachine]

Pinging @elastic/kibana-data-discovery (Team:DataDiscovery)

[kertal]

FYI @lukasolson