Add Sites Renderer service to Docker Compose and implement public endpoint for site definitions

- Introduced `igny8_sites` service in `docker-compose.app.yml` for serving deployed public sites.
- Updated `SitesRendererAdapter` to construct deployment URLs dynamically based on environment variables.
- Added `SiteDefinitionView` to provide a public API endpoint for retrieving deployed site definitions.
- Enhanced `loadSiteDefinition` function to prioritize API calls for site definitions over filesystem access.
- Updated frontend to utilize the new API endpoint for loading site definitions.

backend/igny8_core/modules/publisher/urls.py

@@ -9,6 +9,7 @@ from igny8_core.modules.publisher.views import (
     PublishingRecordViewSet,
     DeploymentRecordViewSet,
     PublisherViewSet,
+    SiteDefinitionView,
 )
 
 router = DefaultRouter()
@@ -19,5 +20,7 @@ router.register(r'', PublisherViewSet, basename='publisher')
 
 urlpatterns = [
     path('', include(router.urls)),
+    # Public endpoint for Sites Renderer
+    path('sites/<int:site_id>/definition/', SiteDefinitionView.as_view(), name='site-definition'),
 ]