Add OWNERS for staging and api

api/ is a copy of pkg/api (same reasoning)
staging/ is the set of people who should be allowing new top level
nested packages + the set of people who can change the staging machinery
code
staging/src/k8s.io/apimachinery/ is the set of core machinery people

staging/OWNERS

@@ -0,0 +1,14 @@
+approvers:
+- lavalamp
+- smarterclayton
+reviewers:
+- lavalamp
+- smarterclayton
+- wojtek-t
+- deads2k
+- caesarxuchao
+- mikedanese
+- liggitt
+- nikhiljindal
+- sttts
+- krousey