Support pointing auditbeat system module at hostfs when running in container

**Describe the enhancement:**
Add support in Auditbeat System module to read from a configurable host filesystem mount when running inside containers, similar to other Beats integrations. Specifically:
Introduce and honor a module-level configuration option (e.g., system.hostfs: /hostfs) that redirects all host reads (e.g., /proc, /etc, /sys paths used by host, login, package, process, user, socket datasets) to the specified mount prefix. Ensure all code paths that access /proc/$pid and related host paths resolve via the configured hostfs prefix, not hardcoded /proc.

**Describe a specific use case for the enhancement or feature:**
Running Auditbeat as a DaemonSet in Kubernetes to collect security/audit events and enrich them with Kubernetes metadata while also using the Auditbeat System module datasets (host, login, package, process, user; socket optionally) from within a container and point reads at the host filesystem mounted into the pod (e.g., /hostfs) so that /proc and other paths resolve to the host, not the container.

Start with the Auditbeat System module configuration and the host, login, package, process, user, and socket dataset paths. Trace every read of /proc, /etc, and /sys, especially /proc/$pid, and compare how other Beats integrations implement hostfs. Done means a module-level hostfs setting redirects all listed host reads to that prefix for container deployments.

Written by the indexing model from the issue text.