refactor: improve service handling and introduce MODE_ASSERT

- Improved get_service_name filter plugin (clearer suffix handling, consistent var names).
- Added MODE_ASSERT flag to optionally execute validation/assertion tasks.
- Fixed systemd unit handling: consistent use of %I instead of %i, correct escaping of instance names.
- Unified on_failure behavior and alarm composer scripts.
- Cleaned up redundant logging, handlers, and debug config.
- Strengthened sys-service template resolution with assert (only active when MODE_ASSERT).
- Simplified timer and suffix handling with get_service_name filter.
- Hardened sensitive tasks with no_log.
- Added conditional asserts across roles (Keycloak, DNS, Mailu, Discourse, etc.).

These changes improve consistency, safety, and validation across the automation stack.

Conversation: https://chatgpt.com/share/68a4ae28-483c-800f-b2f7-f64c7124c274

group_vars/all/01_modes.yml

@@ -6,4 +6,5 @@ MODE_UPDATE:  true  # Executes updates
 MODE_BACKUP:  true  # Activates the backup before the update procedure
 MODE_CLEANUP: true  # Cleanup unused files and configurations
 MODE_DEBUG:   false # This enables debugging in ansible and in the apps, You SHOULD NOT enable this on production servers
-MODE_RESET:   false # Cleans up all Infinito.Nexus files. It's necessary to run to whole playbook and not particial roles when using this function.
+MODE_RESET:   false # Cleans up all Infinito.Nexus files. It's necessary to run to whole playbook and not particial roles when using this function.
+MODE_ASSERT:  false # Executes validation tasks during the run.