Add macOS support to quickstart scripts

[agullon]

Description

The quickstart and quickclean scripts currently only support Linux. Add macOS support so users can run MicroShift in a bootc container on macOS via a Podman machine.

Requirements

• Detect macOS (uname -s == Darwin) and adjust behavior accordingly
• Use podman machine ssh to manage LVM inside the Podman machine VM
• Validate that the Podman machine is running in rootful mode
• Guard Linux-only commands (modprobe, rpm, systemctl, etc.)
• Make container name configurable via CONTAINER_NAME env var
• Update README OS support table

Implementation

PR #220