Refactor docker compose exec usage

Introduce centralized variables:
- docker_compose_command_base
- docker_compose_command_exec

Replaced hardcoded 'docker compose exec' with '{{ docker_compose_command_exec }}'
across multiple roles (BigBlueButton, EspoCRM, Friendica, Listmonk, Mailu, Matrix, OpenProject).
Ensures consistent environment file loading and reduces duplicated code.

Details: https://chatgpt.com/share/68d6a276-19d0-800f-839d-d191d97f7c41

roles/web-app-listmonk/tasks/main.yml

@@ -20,7 +20,7 @@
 - meta: flush_handlers
 
 - name: Check if listmonk database is already initialized
-  command: docker compose exec -T {{ database_host }} psql -U {{ database_username }} -d {{ database_name }} -c "\dt"
+  command: '{{ docker_compose_command_exec }} -T {{ database_host }} psql -U {{ database_username }} -d {{ database_name }} -c "\dt"'
   register: db_tables
   changed_when: false
   failed_when: false