feat(nextcloud): enable custom Alpine-based Whiteboard image with Chromium & ffmpeg support

- Added role tasks to deploy templated Dockerfile for Whiteboard service
- Configured build context and custom image name (nextcloud_whiteboard_custom)
- Increased PID limits and shm_size for stable recording
- Adjusted user ID variable naming consistency
- Integrated path_join for service directory variables
- Fixed build permissions (install as root, revert to nobody)

Reference: ChatGPT conversation https://chatgpt.com/share/68f771c6-0e98-800f-99ca-9e367f4cd0c2

roles/web-app-nextcloud/templates/docker-compose.yml.j2

@@ -67,8 +67,12 @@
   {{ service_name }}:
 {% set container_port = NEXTCLOUD_WHITEBOARD_PORT_INTERNAL %}
 {% include 'roles/docker-container/templates/base.yml.j2' %}
+    build:
+      context: .
+      dockerfile: {{ NEXTCLOUD_WHITEBOARD_SERVICE_DOCKERFILE }}
+    pull_policy: never
 {% include 'roles/docker-container/templates/healthcheck/nc.yml.j2' %}
-    image: "{{ NEXTCLOUD_WHITEBOARD_IMAGE }}:{{ NEXTCLOUD_WHITEBOARD_VERSION }}"
+    image: "{{ NEXTCLOUD_WHITEBOARD_CUSTOM_IMAGE }}"
     container_name: {{ NEXTCLOUD_WHITEBOARD_CONTAINER }}
     volumes:
       - whiteboard_tmp:/tmp
@@ -76,6 +80,7 @@
 
     expose:
       - "{{ container_port }}"
+    shm_size: 1g
     networks:
       default:
         ipv4_address: 192.168.102.71