Refactor MariaDB and PostgreSQL roles for Ansible 2.20 compatibility and Infinito.Nexus conventions

- Replace legacy docker_container-based MariaDB deployment with docker-compose based workflow
- Add custom Dockerfile and docker-compose templates for MariaDB
- Split MariaDB command into separate arguments to avoid entrypoint parsing errors
- Introduce MARIADB_CUSTOM_IMAGE and MARIADB_EXPOSE_LOCAL variables
- Add docker_compose_flush_handlers to ensure correct handler execution on first run
- Replace utils/once/finalize.yml with utils/once/flag.yml for new run-once semantics
- Align variable naming with Infinito.Nexus UPPERCASE conventions
- Fix PostgreSQL custom image variable name (POSTGRES_CUSTOM_IMAGE_NAME → POSTGRES_CUSTOM_IMAGE)
- Remove obsolete flush_handlers var injection in svc-db-postgres/tasks/main.yml
- General cleanup after migration from Ansible 2.18 → 2.20

Conversation reference:
https://chatgpt.com/share/69306c81-9934-800f-b317-f53a8f246a73

roles/svc-db-postgres/tasks/01_core.yml

@@ -8,10 +8,11 @@
   vars:
     docker_network_name:    "{{ POSTGRES_NETWORK_NAME }}"
     docker_network_subnet:  "{{ POSTGRES_SUBNET }}"
+    docker_compose_flush_handlers: true
 
 - name: install python-psycopg2
   community.general.pacman:
     name: python-psycopg2
     state: present
 
-- include_tasks: utils/once/finalize.yml
+- include_tasks: utils/once/flag.yml