Update OWNERS

pkg/volume/downwardapi/OWNERS

 approvers:
 - pmorie
-- sdminonne
+- saad-ali
+- thockin
+- matchstick
 reviewers:
+- ivan4th
+- rata
+- sjenning
 - thockin
 - smarterclayton
-- caesarxuchao
+- deads2k
+- brendandburns
+- derekwaynecarr
+- bprashanth
 - pmorie
 - saad-ali
-- pwittrock
-- timstclair
-- feiskyer
-- markturansky
-- fgrzadkowski
+- justinsb
+- jsafrane
+- rootfs
 - jingxu97
-- fabioy
-- aveshagarwal
-- resouer
-- david-mcmahon
-- tmrts
-- ivan4th
-- rata
-- sdminonne
-- swagiaal
-- chakri-nelluri
+- rkouj
+- msau42