Using a separate directory allows easier backups
(only need to back up the Ansible playbook configuration and the
bridge's `./data` directory).
The playbook takes care of migrating an existing database file
from the base directory into the `./data` directory.
In the future, we can also mount the configuration read-only,
to ensure the bridge won't touch it.
For now, mautrix-facebook is keen on rebuilding the `config.yaml`
file on startup though, so this will have to wait.
Related to #193, but for the Facebook bridge.
(other bridges can be changed to do the same later).
This patch makes the bridge configuration entirely managed by the
Ansible playbook. The bridge's `config.yaml` and `registration.yaml`
configuration files are regenerated every time the playbook runs.
This allows us to apply updates to those files and to avoid
people having to manage the configuration files manually on the server.
-------------------------------------------------------------
A deficiency of the current approach to dumping YAML configuration in
`config.yaml` is that we strip all comments from it.
Later on, when the bridge actually starts, it will load and redump
(this time with comments), which will make the `config.yaml` file
change.
Subsequent playbook runs will report "changed" for the
"Ensure mautrix-facebook config.yaml installed" task, which is a little
strange.
We might wish to improve this in the future, if possible.
Still, it's better to have a (usually) somewhat meaningless "changed"
task than to what we had -- never rebuilding the configuration.
