libvirt_manager: Add boot_order configuration support

[hjensas]

Add support for configuring VM boot device priority via boot_order parameter. Accepts list of 'hd'/'disk' and 'network' in desired boot order. Boot order is applied after device attachment.

Example:
boot_order: ['hd', 'network'] # Try disk first, then PXE

Includes molecule test validating domain XML boot order attributes.

Assisted-By: Claude Code/claude-sonnet-4

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✔️ openstack-k8s-operators-content-provider SUCCESS in 1h 55m 37s
✔️ podified-multinode-edpm-deployment-crc SUCCESS in 1h 18m 01s
✔️ cifmw-crc-podified-edpm-baremetal SUCCESS in 1h 42m 03s
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