This reworks the codimd role, which was already providing HedgeDoc, with
a role that is also called hedgedoc. This is a BREAKING CHANGE. One has
to adjust all role variables in existing setups to be prefixed with
`hedgedoc_` instead of `codimd_`. Also one should make sure that all
data is moved into the new directory locations if relying on defaults.
The default install directory changed from `/var/srv/codimd` to
`/var/srv/hedgedoc`.