[FEATURE] cluster lifecycle hooks

[inercia]

It would be nice to provide some hooks for the lifecycle of the k3d clusters. These hooks would be invoked, for example, after a cluster is created, before a cluster is destroyed, after the registry is created, etc. They would receive some information from k3d in environment variables.

For example, in the k3d config file located at $HOME/.config/k3d/config:

hooks:
  post-create: $HOME/.kd3/post-create.sh

And post-create.sh:

#!/bin/sh
# input: some variables like K3D_CLUSTER_NAME, K3D_MASTER_IP, K3D_CLUSTER_IPS, etc

dns_server="" # TODO: calculate the DNS server from $K3D_CLUSTER_IPS

# route all the 10.0.x.x traffic to the cluster via the master
sudo ip route add $K3D_CLUSTER_IPS via $K3D_MASTER_IP

# this would resolve (from the host) all the services running in this k3d cluster
# with the DNS server inside the cluster
cat<<EOF > /etc/NetworkManager/dnsmasq.d/$K3D_CLUSTER_NAME.conf
server=/$K3D_CLUSTER.local/$dns_server
local=/$K3D_CLUSTER.local/ 
EOF

Depends on #204

[iwilltry42]

We have NodeHookActions now, which have yet to be "opened up" for general usage.