Refactor: remove legacy update-docker role and references

Details:
- Removed update-docker role (README, meta, vars, tasks, script)
- Cleaned references from group_vars, update-compose, and docs
- Adjusted web-app-matrix role (removed @todo pointing to update-docker)
- Updated administrator guide (update-docker no longer mentioned)

Ref: https://chatgpt.com/share/68bbeff1-27a0-800f-bef3-03ab597595fd

roles/web-app-matrix/tasks/01_docker.yml

@@ -67,7 +67,6 @@
   notify: docker compose up
 
 # Pull image when update is wished. 
-# @todo This should be moved to update-docker
 - name: docker compose pull
   command:
     cmd: docker-compose -p "{{ MATRIX_PROJECT }}" pull