Mark KEP as implementable, add feature gate and graduation criteria

keps/sig-node/20190221-initializationFailureThreshold-health-probes.md

@@ -13,7 +13,7 @@ approvers:
 editor: TBD
 creation-date: 2019-02-21
 last-updated: 2019-04-12
-status: provisional
+status: implementable
 see-also:
 replaces:
 superseded-by:
@@ -36,17 +36,19 @@ superseded-by:
       - [Stateless kubelet](#stateless-kubelet)
   - [Design Details](#design-details)
     - [Test Plan](#test-plan)
+    - [Feature Gate](#feature-gate)
+    - [Graduation Criteria](#graduation-criteria)
   - [Implementation History](#implementation-history)
 
 [Tools for generating]: https://github.com/ekalinin/github-markdown-toc
 
 ## Release Signoff Checklist
 
 - [x] kubernetes/enhancements issue in release milestone, which links to KEP (this should be a link to the KEP location in kubernetes/enhancements, not the initial KEP PR)
-- [ ] KEP approvers have set the KEP status to `implementable`
-- [ ] Design details are appropriately documented
-- [ ] Test plan is in place, giving consideration to SIG Architecture and SIG Testing input
-- [ ] Graduation criteria is in place
+- [X] KEP approvers have set the KEP status to `implementable`
+- [X] Design details are appropriately documented
+- [X] Test plan is in place, giving consideration to SIG Architecture and SIG Testing input
+- [X] Graduation criteria is in place
 - [ ] "Implementation History" section is up-to-date for milestone
 - [ ] User-facing documentation has been created in [kubernetes/website], for publication to [kubernetes.io]
 - [ ] Supporting documentation e.g., additional design documents, links to mailing list discussions/SIG meetings, relevant PRs/issues, release notes
@@ -143,6 +145,17 @@ The following test cases can be covered by calling the `fakeExecProber` a number
 - the container is killed after `failureThreshold` once it has initialized (emulated by calling `fakeExecProber{probe.Success, nil}` once) with total probes > `initializationFailureThreshold`
 - the container is killed after `failureThreshold` once it has initialized (emulated by calling `fakeExecProber{probe.Success, nil}` once) with total probes < `initializationFailureThreshold`
 
+### Feature Gate
+
+- Expected feature gate key: `AdditionalProbeParameters`
+- Expected default value: `false`
+
+### Graduation Criteria
+
+- Alpha: Initial support for `initializationFailureThreshold` in Probes added. Disabled by default.
+- Beta:  Enabled by default with default value of `failureThreshold`.
+- Stable:  Enabled by default with default value of `failureThreshold`.
+
 ## Implementation History
 
 - 2018-11-27: prototype implemented in PR [#71449] under review