As a systems administrator managing large-scale container deployments, I need to be able to configure policies for all rootless containers on a system without requiring modifications to individual user-specific configuration files.

Background:
Currently, rootless container configurations are limited to user-specific files (~/.config/containers/containers.conf), which creates challenges for enterprise environments where administrators need to enforce system-wide policies while still allowing users to customize their container runtime behavior.

Solution:
Implement a dedicated configuration path hierarchy for rootless containers that allows administrators to set system-wide defaults while preserving user override capabilities.

Design Reference:
System-wide rootless containers.conf Design Document

Acceptance Criteria:

• Add new configuration file search path specifically for rootless users
• Implement support for /etc/containers/containers.rootless.conf as the primary system-wide rootless configuration file
• Add support for a directory-based configuration approach for per-user administrative configs
• Ensure system-wide rootless configuration is loaded before user's ~/.config/containers/containers.conf
• Verify that user's ~/.config/containers/containers.conf can override system-wide rootless configuration settings
• Update documentation to explain:
  • New configuration file locations
  • Configuration precedence order
  • Usage examples for both administrators and end-users