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

Kubernetes-commit: 32cbeaf516aeca28433d52a8dfa384727c9ee754

OWNERS

@@ -0,0 +1,42 @@
+approvers:
+- lavalamp
+- smarterclayton
+- deads2k
+- sttts
+- liggitt
+- caesarxuchao
+reviewers:
+- thockin
+- lavalamp
+- smarterclayton
+- wojtek-t
+- deads2k
+- derekwaynecarr
+- caesarxuchao
+- mikedanese
+- liggitt
+- nikhiljindal
+- bprashanth
+- gmarek
+- erictune
+- davidopp
+- sttts
+- zmerlynn
+- luxas
+- roberthbailey
+- ncdc
+- timstclair
+- yifan-gu
+- timothysc
+- feiskyer
+- soltysh
+- piosz
+- jbeda
+- dims
+- errordeveloper
+- madhusudancs
+- hongchaodeng
+- krousey
+- vmarmol
+- fgrzadkowski
+- xiang90