Ability to open layout (json file) directly in app

[jtbandes]

For parity with rviz -d config.rviz, it would be nice to be able to launch Studio with foxglove-studio -l layout.json or similar.

Related: #192 & foxglove/studio#2117 (loading layouts from remote/hosted sources)

[defunctzombie]

Is the idea here that you would keep a layout file in your repo? Do you think this would also update layout changes back to that file? What would this do if you are signed in?

[jtbandes]

It would be especially useful for robotics toolkits/projects that want to distribute an example layout. The simplest behavior would be to just create a new layout each time it's invoked this way. What rviz does is treat the current layout as unsaved and prompts you to save when you try to open a different layout or close the app.