feat: web healthcheck returns 503 status code if database is unavailable

docker-compose.yml

@@ -33,12 +33,11 @@ services:
     ports:
       - "8081:80"
     depends_on:
-      data_handler:
+      db:
         condition: service_started
     # all the way zoomed out, with hamburg at the center, at least one camera should be returned
     healthcheck:
-      test: >
-        ["CMD", "curl -s 'http://localhost/camera.php?bbox=-92.52991540527346,30.683278176916133,131.7689595947266,72.87186315234298&zoom=4&width=2552&height=867' | grep '^\[.+\]$'"]
+      test: ["CMD", "curl", "-f", "http://localhost/sync-state.php"]
       interval: 10s
       timeout: 5s
       start_period: 30s