Merge pull request #60998 from jpbetz/etcd-3.1.12

Automatic merge from submit-queue. If you want to cherry-pick this change to another branch, please follow the instructions <a href="https://github.com/kubernetes/community/blob/master/contributors/devel/cherry-picks.md">here</a>.

Bump to etcd 3.1.12 to pick up critical fix

etcd [3.1.12](https://github.com/coreos/etcd/releases/tag/v3.1.12) (as well as 3.2.17 and 3.3.2) was released yesterday to fix a bug critical to kubernetes:

Fix [mvcc "unsynced" watcher restore operation](etcd-io/etcd#9297).
- "unsynced" watcher is watcher that needs to be in sync with events that have happened.
- That is, "unsynced" watcher is the slow watcher that was requested on old revision.
- "unsynced" watcher restore operation was not correctly populating its underlying watcher group.
- Which possibly causes [missing events from "unsynced" watchers](etcd-io/etcd#9086).

This will be backported to 1.9 as well.

Release note:
```release-note
Upgrade the default etcd server version to 3.1.12 to pick up critical etcd "mvcc "unsynced" watcher restore operation" fix.
```

cc @gyuho @wojtek-t @shyamjvs @timothysc @jdumars

Kubernetes-commit: b651ed5ea7331139fc39ea84a55b0261c6b3f000