Add `hostname` propagation to `ironcore-net` `NetworkInterfaces`

[afritzler]

Summary

Annouce the Machine name as the hostname of the VM. This can be now achieved by propagating the hostname to the ironcore-net NetworkInterface via the apinet network plugin.

Tasks

• Add hostname field when creating the ironcore-net NetworkInterface
• Ensure the correct behaviour by extending the existing test suite

/ref ironcore-dev/ironcore-net#400