Improve the default panel size (#9775)

The default panel size is almost always too small for anyone’s needs.
Using half the width per vis seems to work better, along with making
slightly taller.

Author: stacey-gammon

src/core_plugins/kibana/public/dashboard/components/panel/lib/panel_state.js

@@ -1,5 +1,5 @@
-export const DEFAULT_PANEL_WIDTH = 3;
-export const DEFAULT_PANEL_HEIGHT = 2;
+export const DEFAULT_PANEL_WIDTH = 6;
+export const DEFAULT_PANEL_HEIGHT = 3;
 
 /**
  * Represents a panel on a grid. Keeps track of position in the grid and what visualization it