Fix /etc/hosts file and add keycloak's NodeHosts entry in k3d-dev.sh script

The k3d-dev.sh script needs to have the /etc/hosts file entries for the other apps in addition to gitlab. This is necessary when using metallb.

Also, add shell scripting for updating coredns's NodeHosts that can be run by the end user.

This script is run by the end user and is in the docs directory, so this is a doc update.