display data pixel boundaries on layer

[alee]

When zoomed in on the map it would be useful to display the pixel boundaries on the layer so people can figure out if the chart data is sensible or what it's taking into account.

To solve this we could:

1. modify the backend https://github.com/openskope/timeseries-service to return additional geo data demarcating the data pixels around the input boundary
2. always render the pixel boundaries in the client ala https://leafletjs.com/examples/choropleth/ (do we pull this from geoserver?)

Please feel free to chime in if I misunderstood anything @tmcphillips @bocinsky ! Thanks 👍