docs: Add IPv6 network pages for standalone DCGM

[mikemckiernan]

Summary

This PR adds IPv6 network pages to both docsets. DCGM is the only component that needs IPv6-specific configuration, and only when it runs as a standalone daemon set: DCGM Exporter then connects to the nvidia-dcgm service on port 5555.

• gpu-operator/install-gpu-operator-ipv6.rst, under Specialized Networks. Helm defaults to dcgm.enabled: false, so most readers need no IPv6 configuration. The page covers the opt-in standalone case.
• openshift/deploy-gpu-ocp-ipv6.rst. On OpenShift, the default ClusterPolicy from the CSV alm-examples sets dcgm.enabled: true. Source: the published v26.7.1 bundle, operators/gpu-operator-certified/26.7.1/manifests/gpu-operator-certified.clusterserviceversion.yaml in redhat-openshift-ecosystem/certified-operators (commit 8fd2c5e). So every IPv6-only OCP cluster needs the dcgm.args override.

The standalone case needs two things:

• An IPv6 bind for the host engine. The DCGM image's default CMD is -n -b 0.0.0.0 --log-level NONE -f -, which listens on IPv4 only. The Operator sets no args by default, and a non-empty dcgm.args replaces the container args entirely (controllers/object_controls.go). So the pages show the full list:

  dcgm:
    enabled: true
    args: ["-n", "-b", "::", "--log-level", "NONE", "-f", "-"]

• GPU Operator v26.7.1 or later. DCGM 4.6.1 changed DcgmIpc::ConnectTcpAsyncImpl to resolve hostnames with AF_UNSPEC instead of forcing AF_INET. Before that, the exporter couldn't resolve nvidia-dcgm to an IPv6 address. Exporter 4.6.1-4.8.4, which ships in v26.7.1, bundles that client library.

I deliberately left out a cross-link from the troubleshooting pages to keep this content out of the way for most readers.

The docs build wasn't run locally, at the reviewer's request. Pre-commit hooks passed. The only other change in gpu-operator/index.rst is a trailing-whitespace fix made by the pre-commit hook.

Link to Devin session: https://nvidia-cloud.devinenterprise.com/sessions/ec15cc48cd754a1eae4ef22eec691b5d
Open in Devin Desktop: https://nvidia-cloud.devinenterprise.com/desktop/session/ec15cc48cd754a1eae4ef22eec691b5d?variant=devin
Requested by: @mikemckiernan

[devin-ai-integration]

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[github-actions]

Documentation preview

https://nvidia.github.io/cloud-native-docs/review/pr-516

[francisguillier]

thanks @mikemckiernan
the changes LGTM.

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