Add GitHub Container Registry authentication to Podman role

- Deploy /etc/containers/auth.json with GHCR credentials
- Support for private container image pulls
- Credentials encrypted in Ansible vault
- Used by devigo and other services pulling from private registries
- Updated documentation with authentication setup

roles/podman/templates/containers.conf.j2

@@ -19,6 +19,9 @@ network_backend = "netavark"
 # Default network for new containers
 default_network = "{{ podman_default_network }}"
 
+# For signing into ghcr.io
+auth_file = "/etc/containers/auth.json"
+
 # =================================================================
 # Storage Configuration  
 # =================================================================
@@ -64,4 +67,4 @@ default_subnet_pools = [
 # - Create service-specific users for container isolation
 # - Use quadlet files for systemd integration  
 # - Create custom networks for multi-container applications
-# - Access host services via host.containers.internal
+# - Access host services via host.containers.internal