Update OWNERS approvers and reviewers: pkg/api

pkg/api/validation/OWNERS

@@ -0,0 +1,41 @@
+reviewers:
+- thockin
+- lavalamp
+- smarterclayton
+- wojtek-t
+- bgrant0607
+- deads2k
+- yujuhong
+- brendandburns
+- derekwaynecarr
+- caesarxuchao
+- vishh
+- mikedanese
+- liggitt
+- nikhiljindal
+- bprashanth
+- gmarek
+- erictune
+- davidopp
+- pmorie
+- sttts
+- quinton-hoole
+- kargakis
+- dchen1107
+- zmerlynn
+- janetkuo
+- justinsb
+- pwittrock
+- roberthbailey
+- timstclair
+- eparis
+- soltysh
+- piosz
+- jsafrane
+- jbeda
+- dims
+- fejta
+- krousey
+- rootfs
+- markturansky
+- vmarmol