Add witness node manual test case

docs/content/manual/hosts/3266-witness-node.md

@@ -0,0 +1,55 @@
+---
+title: Cluster with Witness Node
+---
+
+Witness node is a lightweight node only runs **etcd** which is not schedulable and also not for workloads. The main use case is to form a quorum with the other 2 nodes.
+
+Kubernetes need at least 3 **etcd** nodes to form a quorum, so Harvester also suggests using at least 3 nodes with similar hardware spec. This witness node feature aims for the edge case that user only have 2 powerful + 1 lightweight nodes thus helping benefit both cost and high availability.
+
+Related Issues
+1. [#3266](https://github.com/harvester/harvester/issues/3266) Support 2 Node / Witness Configuration
+1. [#4840](https://github.com/harvester/harvester/issues/4840) [ENHANCEMENT] various witness mode related enhancement
+
+
+
+## References
+* HLD: https://github.com/harvester/harvester/blob/master/enhancements/20231113-witness-node-support.md
+* `rancher-vcluster` addon: https://docs.harvesterhci.io/v1.3/advanced/addons/rancher-vcluster
+
+## Verification Steps
+1. Setup a 2 nodes cluster with default installation role
+   ![image](https://github.com/harvester/harvester/assets/2773781/f2bb5362-9029-4ee3-a8b5-35af2bc10d5d)
+1. Check nodes' role
+   * **node-0**: Management node
+   * **node-1**: Compute node (quorum yet)
+   ![image](https://github.com/harvester/harvester/assets/2773781/53121fb0-89b6-4a7a-8bc7-9db41441b1b8)
+1. Setup and join 3rd node with witness role
+   ![image](https://github.com/harvester/harvester/assets/2773781/0aa70dba-5d7b-4fcf-935c-1b4fad505ae3)
+1. Check nodes' role
+   * **node-0**: Management node
+   * **node-1**: Management node (Reach quorum, promoted)
+   * **node-2**: Witness node
+   ![image](https://github.com/harvester/harvester/assets/2773781/1b43dd2c-3b7f-4f2d-8fa6-ffd2f4814b00)
+1. Create a VM using default storage class `harvester-longhorn` with some test data
+   * Volume should be `Ready` but `Degraded` since replica count is NOT satisfied (expect 3 but only 2 management nodes)
+     ![image](https://github.com/harvester/harvester/assets/2773781/d8d7fa01-c3ac-49cb-8afa-08df42c6a2dd)
+   * Can NOT migrate VM to witness node
+     ![image](https://github.com/harvester/harvester/assets/2773781/0a10825d-91e9-4d1c-993d-89c84708d2fa)
+   * Can take snapshot
+   * Can take backup
+1. Enable `rancher-vcluster`
+   * Join Harvester to Rancher
+   * Create Nginx deployment
+   * Create load balancer for deployment
+
+## Expected Results
+1. Restart VM, VM and its data should still fine.
+1. Restore snapshot, VM and its data should still fine.
+1. Restore backup, VM and its data should still fine.
+1. `rancher-vcluster` works.
+   ![image](https://github.com/harvester/harvester/assets/2773781/3424370a-3f47-47dd-8225-ee8080df8e01)
+
+
+## Notes
+1. Except manual setup, another approach is harvester setup configuration
+   https://docs.harvesterhci.io/v1.3/install/harvester-configuration#installrole