Add geo data point marker pin image display

[RandomFractals]

see changes in #8 for the initial marker clusters setup

[RandomFractals]

try this solution for the leaflet marker image loading from webpack bundle: Leaflet/Leaflet#4968 (comment)

and see docs: https://leafletjs.com/examples/custom-icons/

or use this simple svg icons solution: https://codepen.io/localhorst/pen/yppoKO

or use our simple blue dot marker solution from this js notebook: https://observablehq.com/@randomfractals/chicago-average-daily-traffic-counts

[RandomFractals]

map with new custom svg marker for locations ... might need to make it larger or reduce marker cluster icon size:

Ideally, should be close to github leaflet map display of geojson: https://github.com/RandomFractals/vscode-leaflet/blob/main/data/geojson/world-cities.geojson

[RandomFractals]

after cluster and pin marker sizing changes: