feat(k3s): add custom tls-san snippets

# K3s

This guide assumes 3 nodes which are already setup with a minimal OS installation and network connectivity. Also make

sure DNS entries are in place for all nodes.

Our examples bellow use the following nodes:

| Node | Role | FQDN | IP Address ^ |

|---|---|---|---|

| proxy | HAProxy loadbalancer | proxy.k3s.siempie.internal | 192.168.10.230 |

| node01 | Master + Worker | node01.k3s.siempie.internal | 192.168.10.231 |

| node02 | Master + Worker | node02.k3s.siempie.internal | 192.168.10.232 |

| node03 | Master + Worker | node03.k3s.siempie.internal | 192.168.10.233 |

Our API and HTTP workloads will be proxied via the HAProxy loadbalancer. The k3s api server will be accessible at

`https://workload.k3s.siempie.internal:6443`. The HAProxy configuration is found

[here](<https://docs.simoncor.net/linux/haproxy>).

## Boostrap k3s with a custom TLS SAN

```bash

# Node 1 (first master)

curl -sfL https://get.k3s.io | sh -s - server \

  --cluster-init \

  --tls-san workload.k3s.siempie.internal \

  --tls-san node01 \

  --tls-san node01.k3s.siempie.internal

# Save token for other nodes

cat /var/lib/rancher/k3s/server/node-token

```

## Join other masters

```bash

# Node 2 and 3 (other masters)

curl -sfL https://get.k3s.io | sh -s - server \

  --server https://node01:6443 \

  --token <token-from-node01> \

  --tls-san workload.k3s.siempie.internal \

  --tls-san node02 \

  --tls-san node02.k3s.siempie.internal

```