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.
Bridges start matrix-synapse.service as a dependency, but
Synapse is sometimes slow to start, while bridges are quick to
hit it and die (if unavailable).
They'll auto-restart later, but .. this still breaks `--tags=start`,
which doesn't wait long enough for such a restart to happen.
This attempts to slow down bridge startup enough to ensure Synapse
is up and no failures happen at all.
