[DCN] Explicitly set network availability zone parameters

[sbekkerm]

This patch explicitly sets the network availability zone parameters to their default values, enabling the configuration of availability zones for DCN sites if needed.

[fultonj]

Run test-kustomization script fails with

examples/dt/dcn/kustomization.yaml: ERROR
Error: accumulating components: accumulateDirectory: "recursed accumulation of path '/home/runner/work/architecture/architecture/dt/dcn/edpm-post-ceph/nodeset': fieldPath `data.ovn.template.ovnController.external-ids.availability-zones` is missing for replacement source ConfigMap.[noVer].[noGrp]/service-values.[noNs]"

https://github.com/openstack-k8s-operators/architecture/actions/runs/11782586725/job/32817945322?pr=440

[fultonj]

/approve
/lgtm

[openshift-ci]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: fultonj, sbekkerm

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[softwarefactory-project-zuul]

Build succeeded (gate pipeline).
https://softwarefactory-project.io/zuul/t/rdoproject.org/buildset/fbfd597a4dc440d69d5f7d76110d4fee

✔️ noop SUCCESS in 0s
✔️ rhoso-architecture-validate-dcn SUCCESS in 3m 19s

[sbekkerm]

/cherrypick 18.0-fr1

[openshift-cherrypick-robot]

@sbekkerm: new pull request created: #446

In response to this:

/cherrypick 18.0-fr1

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