Add MapTiler library for Leaflet

@maptiler/leaflet-maptilersdk

This will allow us to display our OpenStreetMap layer in
vector form rather than with raster tiles. See:

https://www.maptiler.com/news/2019/02/what-are-vector-tiles-and-why-you-should-care/

For more details on using Maptiler, particularly with
Leaflet:

- https://docs.maptiler.com/leaflet/examples/vector-tiles-in-leaflet-js/
- https://docs.maptiler.com/sdk-js/
- https://github.com/maplibre/maplibre-gl-leaflet/
- https://github.com/maptiler/leaflet-maptilersdk

app/javascript/maps.js

@@ -1,4 +1,5 @@
 import L from "leaflet";
+import "@maptiler/leaflet-maptilersdk";
 
 document.addEventListener("turbo:load", function () {
   const mapEle = document.querySelector("#map");

config/initializers/content_security_policy.rb

@@ -12,6 +12,7 @@
   policy.img_src :self, :https, :data
   policy.object_src :none
   policy.script_src :self, :https
+  policy.worker_src :self, :blob
 
   # allow styling for the Turbo progress bar
   policy.style_src("'sha256-WAyOw4V+FqDc35lQPyRADLBWbuNK8ahvYEaQIYF1+Ps='", :self, :https)

package.json

@@ -14,6 +14,7 @@
   "devDependencies": {
     "@eslint/eslintrc": "^3.1.0",
     "@eslint/js": "^9.11.1",
+    "@maptiler/leaflet-maptilersdk": "^2.0.0",
     "esbuild": "^0.24.0",
     "eslint": "^9.0.0",
     "eslint-config-prettier": "^9.0.0",