Add an option to not automatically open Proof View

[varkor]

When I'm looking through a list of search results, for example, creating a new Proof View for each file I open spawns a lot of unnecessary extra panes. It'd be nice to either have an option to disable this or, even better (though perhaps not possible) replace whatever current proof view there is with the new one, to stop the propagation.

Such a setting seems to exist (https://github.com/siegebell/vscoq/blob/master/client/package.json#L102-L107), but VS Code doesn't seem to recognise the option.