Update generated client to Kubernetes v1.36 (SDK 20.0)

[Copilot]

Tracks the upstream v1.36 API surface and bumps the SDK accordingly (refs #1712).

• Generation inputs: csharp.settings → KUBERNETES_BRANCH=v1.36.0.
• Generated artifacts: swagger.json regenerated from the processed v1.36 spec (info.version is now v1.36.0).
• Versioning & docs: version.json raised to 20.0; README compatibility table extended with the 20.0 / 1.36 row.

Generator caveat

swagger.json was regenerated using kubernetes-client/gen's openapi/preprocess_spec.py pinned to commit dde176f — the same generator state used for the v1.35 PR (#1712).

A more recent gen change (commit 71843ee) unconditionally injects apidiscovery.k8s.io/v2{,beta1} definitions whose $refs point to io.k8s.apimachinery.pkg.apis.meta.v1.GroupVersionKind. That type is no longer present in the upstream v1.36 OpenAPI spec, leaving dangling refs that cause KubernetesClientSourceGenerator to fail to initialize:

warning CS8784: Generator 'KubernetesClientSourceGenerator' failed to initialize.
  ... 'Could not resolve the path
        '#/definitions/io.k8s.apimachinery.pkg.apis.meta.v1.GroupVersionKind'.'

Pinning the gen revision sidesteps this; a follow-up in kubernetes-client/gen should fix the dangling ref before adopting newer gen revisions here.

[Copilot]

Pull request overview

Updates the Kubernetes C# client generation inputs and project metadata to align with the Kubernetes v1.36 API surface and bump the SDK major version to 20.0.

Changes:

• Bump SDK version to 20.0 via Nerdbank.GitVersioning (version.json).
• Update generation target to KUBERNETES_BRANCH=v1.36.0 (csharp.settings).
• Extend the README compatibility matrix with the 20.0 / 1.36 entry.

Reviewed changes

Copilot reviewed 3 out of 4 changed files in this pull request and generated no comments.

File	Description
version.json	Raises SDK version to 20.0 for the v1.36 client generation release.
csharp.settings	Points the generator at Kubernetes v1.36.0.
README.md	Adds the 20.0 / 1.36 row to the version compatibility table.

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[brendandburns]

/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

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