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

Kubernetes-commit: f306a0dbb4a462e2ac5882196e7276a0c890b219

.import-restrictions

@@ -1,10 +1,5 @@
-{
-  "Rules": [
-    {
-      "SelectorRegexp": "k8s[.]io/kubernetes",
-      "ForbiddenPrefixes": [
-        ""
-      ]
-    }
-  ]
-}
+rules:
+  # prevent import of k8s.io/kubernetes
+  - selectorRegexp: k8s[.]io/kubernetes
+    forbiddenPrefixes:
+      - ''