feat: add OWNERS files for flagz server and api with approvers and reviewers

Kubernetes-commit: 256591520a552cda01b75eca08b1715a5f35e398

Author: yongruilin

pkg/server/flagz/OWNERS

@@ -0,0 +1,7 @@
+approvers:
+ - sig-instrumentation-approvers
+ - sig-api-machinery-approvers
+reviewers:
+ - sig-instrumentation-reviewers
+labels:
+ - sig/instrumentation

pkg/server/flagz/api/OWNERS

@@ -0,0 +1,11 @@
+# Disable inheritance as this is an api owners file
+options:
+ no_parent_owners: true
+approvers:
+ - api-approvers
+reviewers:
+ - api-reviewers
+ - sig-instrumentation-reviewers
+labels:
+ - kind/api-change
+ - sig/instrumentation