etcd: infinite reconnect loop when using JWT authentication

[awly]

Our etcd client library is missing etcd-io/etcd#12165

This causes teleport to go into an infinite reconnect loop within its etcd client once the initial JWT expires.
This situation only happens when:

• teleport uses usrname/password authentication for etcd
• etcd cluster is configured with --auth-token=jwt (https://etcd.io/docs/v3.3/op-guide/configuration/#--auth-token)

Update the etcd client library if possible.
The fallback would be some hacky grpc interceptor hook into the etcd client to detect this and recreate the entire client.