convert .import-restrictions to yaml

yaml has comments, so we can explain why we have certain rules or
certain prefixes

for those files that weren't already commented yaml, I converted them to
yaml and took a best guess at comments based on the PRs that introduced
or updated them

pkg/kubemark/.import-restrictions

@@ -1,13 +1,6 @@
-{
-	"Rules": [
-	  {
-		"SelectorRegexp": "k8s[.]io/kubernetes/cmd",
-		"AllowedPrefixes": [
-		    "k8s.io/kubernetes/cmd/kube-proxy/app",
-		    "k8s.io/kubernetes/cmd/kubelet/app"
-		],
-		"ForbiddenPrefixes": [
-		]
-	  }
-	]
-}
+rules:
+  # override pkg/ import restriction on cmd/ for kubemark
+  - selectorRegexp: k8s[.]io/kubernetes/cmd
+    allowedPrefixes:
+      - k8s.io/kubernetes/cmd/kube-proxy/app
+      - k8s.io/kubernetes/cmd/kubelet/app