* feat: implement setting mtu for virtio network device
See https://git.proxmox.com/?p=qemu-server.git;a=commit;h=61a14cde8d568e552d3deaab2da76b479b8aca7b
* fix: split extractNetworkModelAndBridge into multiple functions
* fix: set maximum mtu to 65520
* test: should not allow mtu less than 1 or more than 65520
* feat: add validating webhook for proxmoxmachine
* fix: remove default mtu