Update K3s to latest engine-1.21

[Oats87]

Proposed Changes

Bump K3s to the latest engine-1.21 commit ID to implement the etcd-member-management controller

Types of Changes

Engine changes

Verification

1. Create a multi-node etcd-backed RKE2 cluster.
2. Perform an etcdctl member list command using a downloaded etcdctl binary from the etcd project on any of the etcd nodes similar to:

etcdctl --cacert=/var/lib/rancher/rke2/server/tls/etcd/server-ca.crt --cert=/var/lib/rancher/rke2/server/tls/etcd/client.crt --key=/var/lib/rancher/rke2/server/tls/etcd/client.key member list -w table

and observe that there should be N etcd members listed, where N is the number of etcd nodes in the cluster.
3. Annotate one of your etcd nodes (preferably not the "bootstrap" node) with the annotation etcd.rke2.cattle.io/remove=true. List/describe the annotations of the node and watch the etcd.rke2.io/removed-node-name annotation be set to the etcd node name that corresponded to the list of nodes in the member list command from above.
4. Re-run the etcdctl member list and observe that the etcd member is NOT listed in the list anymore. Additionally, looking at the logs of etcd and notice it is crashing.

Linked Issues

#1816

Further Comments

[briandowns]

LGTM

[briandowns]

Here's the k3s diff: k3s-io/k3s@f2c7882...34de120