feat(nextcloud): Add imaginary container for thumbnails

roles/nextcloud/templates/docker-stack.yml.j2

@@ -142,6 +142,24 @@ services:
     networks:
       - backend
 
+  # from https://okxo.de/speed-up-nextcloud-preview-generation-with-imaginary/
+  # and https://github.com/nextcloud/all-in-one/tree/main/Containers/imaginary
+  imaginary:
+    image: nextcloud/aio-imaginary:latest
+    environment:
+      - PORT=9000
+    healthcheck:
+      test: ["CMD", "/healthcheck.sh"]
+      interval: 1m
+      timeout: 10s
+      retries: 3
+      start_period: 1m
+    command: -return-size -max-allowed-resolution 222.2 -concurrency 50 -enable-url-source -log-level debug
+    cap_add:
+      - CAP_SYS_NICE
+    networks:
+      - backend
+
   # metrics:
   #   image: telegraf
   #   hostname: "${HOSTNAME:-vmi352583.contaboserver.net}"