add proposal that shell access to node

sig-edge/concepts-and-designs/shell-access-to-node-proposal.md

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+# Motivation
+This function can make it easier for us to manage the host on Web UI, 
+it could be for maintenance, configuration inspection, log collection, or other troubleshooting operations.
+
+# Goals
++ Add a button in the nodes interface to open the terminal linked to the node
++ It can work on k8s cluster nodes and edge nodes
+
+# Design detail
+## Technology selection
+
+At first, I planned to use edgemesh's SSH tunnel proxy, but it can't work on k8s cluster nodes.
+Later, at the [suggestion](https://github.com/kubesphere/kubesphere/issues/4569) of the community I use nsenter to do this. 
+The nsenter is a small program from util-linux package, that can run program with namespaces (and cgroups) of other processes. Exactly what we need!
+
+## Workflow
+![shell-access-to-node](../images/shell-access-to-node.png)
+
+**step0:**  
+The client initiates a terminal link request to the ks-apiserver
+
+**step1:**  
+ks-apiserver will perform permission verification after accepting the request, If the user has permission to create a pod it will creates an nsenter instance on the corresponding node
+
+**step2:**  
+When the nsenter state changes to running, connect to the container through kubectl exec(ps: Using kubesphere's encapsulated method)
+
+**step3:**  
+Delete the nsenter instance when the client disconnects
+
+## Other Details
+###Condition monitoring  
+Because the instance creation takes time and the front-end page can be accessed concurrently, I used for true {getpodstatus()} to detect it instead of list watch.This eliminates the need to notify two threads in one event.
+
+### When to delete an nsenter
+At present, I use atomic counting to delete instances when no client is connected to nsenter. Whether the function of scheduled deletion is required?
+If necessary, We need to add the detection of whether the client is active in the original program
+
+
+# Demo
+
+### shell access to k8s cluster node
+![step 1](../images/shell-access-to-node-demo-1.png)
+![step 2](../images/shell-access-to-node-demo-2.png)
+![step 3](../images/shell-access-to-node-demo-3.png)
+
+### Exit automatic deletion
+![step 4](../images/shell-access-to-node-demo-4.png)
+
+### shell access to edge node
+![step 5](../images/shell-access-to-node-demo-5.png)
+The terminal button is not displayed when the node status is incorrect
+![step 6](../images/shell-access-to-node-demo-6.png)