Support FeatureCollection and MultiPolygon in geozones

We're reworking the format validation to correctly interpret feature
collection, feature, and geometry, according to RFC 7946 [1].

Since Leaflet interprets GeoJSON format, we're rendering the GeoJSON as
a layer instead of as a set of points. For that, we're normalizing the
GeoJSON to make sure it contains either a Feature or a
FeatureCollection. We're also adding the Leaflet images to the assets
path so the markers used for point geometries are rendered correctly.

Note we no longer allow a GeoJSON containing a geometry but not a
defined type. Since there might be invalid GeoJSON in existing Consul
Democracy databases, we're normalizing these existing geometry objects
to be part of a feature object.

We're also wrapping the outline points in a FeatureCollection object
because most of the large GIS systems eg ArcGIS, QGIS export geojson as
a complete FeatureCollection.

[1] https://datatracker.ietf.org/doc/html/rfc7946

Co-authored-by: Javi Martín <javim@elretirao.net>

spec/system/admin/geozones_spec.rb

@@ -110,8 +110,16 @@ describe "Admin geozones", :admin do
 
   scenario "Show polygons when a heading is associated with a geozone" do
     Setting["feature.map"] = true
+    geojson = <<~JSON
+      {
+        "type": "Feature",
+        "geometry": {
+          "type": "Polygon",
+          "coordinates": [[[-0.1, 51.5], [-0.2, 51.4], [-0.3, 51.6]]]
+        }
+      }
+    JSON
 
-    geojson = '{ "geometry": { "type": "Polygon", "coordinates": [[-0.1,51.5],[-0.2,51.4],[-0.3,51.6]] } }'
     geozone = create(:geozone, name: "Polygon me!")
     budget = create(:budget)
     group = create(:budget_group, budget: budget)
@@ -145,7 +153,16 @@ describe "Admin geozones", :admin do
 
   scenario "Show polygons on geozone admin view" do
     Setting["feature.map"] = true
-    geojson = '{ "geometry": { "type": "Polygon", "coordinates": [[-0.1,51.5],[-0.2,51.4],[-0.3,51.6]] } }'
+    geojson = <<~JSON
+      {
+        "type": "Feature",
+        "geometry": {
+          "type": "Polygon",
+          "coordinates": [[[-0.1, 51.5], [-0.2, 51.4], [-0.3, 51.6]]]
+        }
+      }
+    JSON
+
     geozone = create(:geozone, name: "Polygon me!", geojson: geojson)
 
     visit admin_geozones_path