[RFE] Implement `cp` command

## Current situation

`kubectl-aks` does not provide any way to copy files into nodes.

## Ideal future situation

Investigate if it could be useful for users to have a command to copy files from host to nodes:

```
$ kubectl aks cp --node aks-agentpool-21361837-vmss000000 /source/path/on/host /destination/path/on/node
```

Start by investigating the current way to do it using the Azure CLI (`az`) and whether the SDK already provides the APIs to replicate it here or not.

Start by investigating how the Azure CLI `az` currently copies files into AKS nodes, then check whether the Azure SDK exposes APIs that can support the proposed `kubectl aks cp` command. Done means determining the viable approach and implementing the host-to-node copy behavior, with its scope clarified from that investigation.

Written by the indexing model from the issue text.