Add --tls-san for join command for servers

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This was a missing part of the HA story, that sets an extra IP or hostname in the TLS cert for the kubelet on each host, so that they can be used interchangeably behind a load-balancer, proxy, inlets or something else.

k3sup join --server \
  --server-ip $SERVER_IP \
  --ip EXTRA_SERVER_IP \
  --tls-san LB_IP

Changelog for 0.12.14:

Commits
e4107dd Add --tls-san for join command for servers by @alexellis
d47b699 Update README.md by @alexellis
8e9af1c Update README.md by @alexellis
638c02d Update caption localk3 to localk3s by @alexellis
438fe71 Update dependencies by @alexellis

Changes: 0.12.13...0.12.14

Generated by Derek