kubeadm-config: include new commands (#8862)

Add notes and includes for these new commands in 1.11:
- kubeadm config print-default
- kubeadm config migrate
- kubeadm config images list
- kubeadm config images pull

Include placeholder generated files for the above.

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

@@ -0,0 +1,5 @@
+PLACEHOLDER FILE UNTIL WE GENERATE THE REAL THING. DO NOT REMOVE FROM 1.11 DOCS BRANCH
+
+### Synopsis
+
+Print a list of images kubeadm will use.

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

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+PLACEHOLDER FILE UNTIL WE GENERATE THE REAL THING. DO NOT REMOVE FROM 1.11 DOCS BRANCH
+
+### Synopsis
+
+Pull images used by kubeadm.

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

@@ -0,0 +1,5 @@
+PLACEHOLDER FILE UNTIL WE GENERATE THE REAL THING. DO NOT REMOVE FROM 1.11 DOCS BRANCH
+
+### Synopsis
+
+migrate config from one version to another.

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

@@ -0,0 +1,5 @@
+PLACEHOLDER FILE UNTIL WE GENERATE THE REAL THING. DO NOT REMOVE FROM 1.11 DOCS BRANCH
+
+### Synopsis
+
+print default config.