Introduce upgrade strategy for workers

[kinarashah]

Worker nodes also respect some kind of upgrade strategy such that not all of them are updated simultaneously. It would include maxUnavailable count, default to 1 for control plane/etcd nodes.

#23777

[sowmyav27]

On master-head - commit id: 926997017

• max_unavailable_worker: 10% is available by default on a cluster
• With default values upgrade_strategy, the sequence of how the upgrade happens in the cluster is given below

- etcd nodes - will upgrade one by one with the etcd components upgrading
- control plane nodes - will upgrade one by one - will be cordoned when this is happening. Control plane components - sidekick, kube-apiserver, kube-controller-manager, kube-scheduler and worker plane components - kubelet, kubeproxy
- etcd nodes will be cordoned - when the worker plane components - kubelet, kubeproxy are getting upgraded
- currently in rancher - worker plane nodes and add ons will get executed/upgraded in parallel.
- Default max_unavailable_worker: 10% so 1 worker node gets upgraded at a time. 

• If Drain is enabled, the nodes are drained.
• Else they go into cordoned state. and then Upgrade and to Active.
• State transition wrt to worker nodes from UI
• When Drain : false

-  Active --> Cordoned (Upgrading message) --> Active

• When Drain: True

-  Active --> Cordoned (Upgrading message) (might not be visible as it might happen really fast --> Draining --> Drained (Upgrading message) --> Active