fix: make valhalla.json bind mount writable

The compose renderer defaults bind mounts to read-only, which broke the valhalla-scripted entrypoint: it runs `valhalla_build_config` at startup and tries to overwrite `/custom_files/valhalla.json`, failing with `OSError: [Errno 30] Read-only file system`. Set `readOnly: false` so the entrypoint can regenerate the config from the env vars (`serve_tiles`, `build_elevation`, etc.) on every start.

Author: Medformatik

services/valhalla/service.json

@@ -31,7 +31,13 @@
   },
   "provides": ["routing-engine"],
   "consumes": [{ "type": "osm-pbf", "mountAt": "/custom_files", "required": true }],
-  "bindMounts": [{ "source": "config/valhalla.json", "target": "/custom_files/valhalla.json" }],
+  "bindMounts": [
+    {
+      "source": "config/valhalla.json",
+      "target": "/custom_files/valhalla.json",
+      "readOnly": false
+    }
+  ],
   "configSchema": {
     "type": "object",
     "properties": {