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/config/main.yml

@@ -82,7 +82,7 @@ docker:
       cpus:                 "1.0"
       mem_reservation:      "256m"
       mem_limit:            "1g"
-      pids_limit:           512
+      pids_limit:           1024
     whiteboard:
       name:                 "nextcloud-whiteboard"
       image:                "ghcr.io/nextcloud-releases/whiteboard"
@@ -92,7 +92,7 @@ docker:
       cpus:                 "0.25"
       mem_reservation:      "128m"
       mem_limit:            "512m"
-      pids_limit:           256
+      pids_limit:           1024
   enabled:  "{{ applications | get_app_conf('web-app-nextcloud', 'features.oidc', False, True, True) }}"   # Activate OIDC for Nextcloud
   # floavor decides which OICD plugin should be used. 
   # Available options: oidc_login, sociallogin