Add a hedgedoc role to install and run a hedgedoc instance.
This will:
- install and configure a postgres instance (ready to receive the hedgedoc schema)
- install and configure a hedgedoc instance
- then configure and run the hedgedoc systemd service
Remains:
- some more configuration options which can be opened later (as we go along i guess)
- certificate part which can be dealt with later
Related to T2827