Join FreeRADIUS server to FreeIPA domain

This is done to automatically issue FreeRADIUS certificates like this

ipa-client-install \
  --hostname "$( hostname --short ).od.freeipa.xyz" \
  --domain "od.freeipa.xyz"  \
  --ntp-pool time.freeipa.xyz \
  --no-ssh \
  --no-sshd \
  --no-sudo \
  --ssh-trust-dns \
  --enable-dns-updates \
  --password=7Qexxxxxxxxxx