Hazard Model GeoJSON Map

Add method to hazard model to return the GeoJSON extent of the NSHM.

Example: https://code.usgs.gov/ghsc/nshmp/nshms/nshm-conus/-/blob/main/map-conus.geojson

mentioned in issue nshmp-haz#536 (closed)

assigned to @bclayton

changed milestone to %NSHM Hazard Tool - Sprint 4

added To Do label

added In Progress label and removed To Do label

mentioned in merge request !308 (merged)

mentioned in commit cdd25f41

closed with merge request !308 (merged)

removed In Progress label