Merge pull request kubernetes#2099 from dashpole/back_to_implementable

Revert part of kubernetes#2098.  Metrics stability is not GA

Author: k8s-ci-robot

keps/sig-instrumentation/20191028-metrics-stability-to-beta.md

@@ -13,7 +13,7 @@ approvers:
 editor: "@brancz"
 creation-date: 2019-10-28
 last-updated: 2020-10-14
-status: implemented
+status: implementable
 stage: beta
 see-also:
   - 20181106-kubernetes-metrics-overhaul