[FEATURE] add ability to add ports to an existing loadbalancer

[iwilltry42]

What

This PR adds the functionality to edit existing nodes.
Primary use case for the ALPHA is adding new port-mappings to existing nodes, primarily the loadbalancer (as it is stateless, making it easier to handle the recreation).

How

We compile a changeset (basically a new node, with only the newly added fields filled), which we add to a copy of the selected target node (with stripped out status fields).
Then we rename the existing/old node, create the new one, stop the old one, start the new one, delete the old one.
If anything goes wrong in the middle of the process, then we'll try to rollback to having the old node ready as before (same name, same ports, etc.).

Why

This allows us to add new port-mappings (and hopefully more at some point) to an existing cluster, e.g. if one forgot to map the http/https ports for ingress when creating the cluster or if there's a new nodePort present, etc.

Change Overview

CLI

• new command k3d node edit NODENAME
  • new flag: --port-add [HOSTPORT:]CONTAINERPORT[/PROTOCOL]
    • e.g. k3d node edit k3d-mycluster-serverlb --port-add 8080:80 to add http port mapping for ingress after creating the cluster

pkg

• new client function NodeEdit

To-Do

• rollback if creation/start of new container failed

Related Issues

#6 (though far from what was discussed there)