Description of problem:
Due to https://bugzilla.redhat.com/show_bug.cgi?id=2179333, any VM connected to a VLAN through a bridge CNI NAD is also connected to the native VLAN 1. This is unintended. We should make sure our users set `"preserveDefaultVlan": false` to prevent this from happening.

Version-Release number of selected component (if applicable):
4.12.5+

How reproducible:
Always

Steps to Reproduce:
1. Create a bridge NAD through the UI

Actual results:
It is created without `"preserveDefaultVlan": false` which causes the issue described above.


Expected results:
The generated NAD contains `"preserveDefaultVlan": false`. Example:
  apiVersion: "k8s.cni.cncf.io/v1"
  kind: NetworkAttachmentDefinition
  metadata:
    name: <bridge-network> 
    annotations:
      k8s.v1.cni.cncf.io/resourceName: bridge.network.kubevirt.io/<bridge-interface> 
  spec:
    config: '{
      "cniVersion": "0.3.1",
      "name": "<bridge-network>", 
      "type": "cnv-bridge", 
      "bridge": "<bridge-interface>", 
      "macspoofchk": true, 
      "vlan": 1,
      "preserveDefaultVlan": false
    }'


Additional info:
This should be changed on all releases starting with 4.12.
The backend bug where this new attribute was introduced: https://bugzilla.redhat.com/show_bug.cgi?id=2179333