Move core api to pkg/apis/core

pkg/apis/core/OWNERS

+approvers:
+- erictune
+- lavalamp
+- smarterclayton
+- thockin
+- liggitt
+# - bgrant0607 # manual escalations only
+reviewers:
+- thockin
+- lavalamp
+- smarterclayton
+- wojtek-t
+- deads2k
+- yujuhong
+- brendandburns
+- derekwaynecarr
+- caesarxuchao
+- vishh
+- mikedanese
+- liggitt
+- nikhiljindal
+- gmarek
+- erictune
+- davidopp
+- pmorie
+- sttts
+- dchen1107
+- saad-ali
+- zmerlynn
+- luxas
+- janetkuo
+- justinsb
+- pwittrock
+- roberthbailey
+- ncdc
+- tallclair
+- yifan-gu
+- eparis
+- mwielgus
+- timothysc
+- soltysh
+- piosz
+- jsafrane
+- jbeda

pkg/apis/core/v1/OWNERS

+reviewers:
+- thockin
+- lavalamp
+- smarterclayton
+- wojtek-t
+- deads2k
+- yujuhong
+- brendandburns
+- derekwaynecarr
+- caesarxuchao
+- vishh
+- mikedanese
+- liggitt
+- nikhiljindal
+- gmarek
+- erictune
+- davidopp
+- pmorie
+- sttts
+- dchen1107
+- saad-ali
+- zmerlynn
+- luxas
+- janetkuo
+- justinsb
+- roberthbailey
+- ncdc
+- tallclair
+- eparis
+- timothysc
+- piosz
+- jsafrane
+- dims
+- errordeveloper
+- madhusudancs
+- krousey
+- jayunit100
+- rootfs
+- markturansky