fix shortcode, add placeholder files to fix deploy failures (#8874)

content/en/docs/reference/setup-tools/kubeadm/generated/kubeadm_alpha_phase_addon_coredns.md

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+PLACEHOLDER FILE UNTIL WE GENERATE THE REAL THING. DO NOT REMOVE FROM 1.11 DOCS BRANCH
+
+### Synopsis
+
+Installs the coredns addon components via the API server.

content/en/docs/reference/setup-tools/kubeadm/generated/kubeadm_upgrade_diff.md

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+
+PLACEHOLDER FILE UNTIL WE GENERATE THE REAL THING. DO NOT REMOVE FROM 1.11 DOCS BRANCH
+
+### Synopsis
+
+diff something or other