Shared cursors on Dashboard Cells

Chronograf 1.x used to share the cursor pointers across all cells on a dashboard, we should bring parity to 2.0. It looks a little something like this:


Use the issue description and attached cursor-sharing GIF as the behavioral reference. Start by locating the dashboard cell cursor-handling entry points and checking how cursor state is scoped between cells. Done means moving a cursor in one dashboard cell visibly shares the corresponding cursor pointer across the other cells, matching the Chronograf 1.x behavior.

Written by the indexing model from the issue text.