enhancement: check default route during installation

[mingshuoqiu]

Problem: RKE2 requires a default route to start, some installations are stuck with no obvious message if there is no default route on the system.

Solution: Check the existence of the default route after applying network settings and stop the installation if no default route found. The check will be applied in both ISO and iPXE installation.

Related Issue: https://github.com/harvester/harvester/issues/5675

Test plan:

1. Set up a DHCP server and enable the iPXE capability which runs w/o option routers x.x.x.x
2. Proceed the Harvester ISO installation with the management network in DHCP mode.
3. Make sure the installer prompt the No default route found message and stop the installation
4. Proceed the iPXE automatic installation with pre-configured Harvester configuration file.
5. Make sure the iPXE automatic installation stops and prompt the No default route found message.