Try to do the signald (0.19.0) data migration automatically

Improvement over e4caf3fa81.

Related to https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/1921

CHANGELOG.md

@@ -1,35 +1,16 @@
 # 2022-07-14
 
-## mautrix-signal upgrade requires manual data migration
+## signald (0.19.0+) upgrade requires data migration
 
 In [Pull Request #1921](https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/1921) we upgraded [signald](https://signald.org/) (used by the mautrix-signal bridge) from `v0.18.5` to `v0.20.0`.
 
-Back in the `v0.19.0` released of signald (which we skipped and migrated straight to `v0.20.0`), a new `--migrate-data` command had been added that migrates avatars, group images, attachments, etc., into the database (those were previously stored in the filesystem).
+Back in the [`v0.19.0` released of signald](https://gitlab.com/signald/signald/-/blob/main/releases/0.19.0.md) (which we skipped and migrated straight to `v0.20.0`), a new `--migrate-data` command had been added that migrates avatars, group images, attachments, etc., into the database (those were previously stored in the filesystem).
 
-If you've been using the mautrix-signal bridge for a while, you may have files stored in the local filesystem, which will need to be upgraded using a `--migrate-data` command when you're upgrading mautrix-signal and signald.
+If you've been using the mautrix-signal bridge for a while, you may have files stored in the local filesystem, which will need to be upgraded.
 
-We don't have a test setup running signald with actual data in it, so we're not sure what the best way to upgrade is. You could try the following steps:
+We attempt to do this data migration automatically every time Signald starts (`matrix-mautrix-signal-daemon.service`) using a `ExecStartPre` systemd unit definition.
 
-1. Update the playbook's source code
+Keep an eye on your Signal bridge and let us know (in our [support room](README.md#support) or in [Pull Request #1921](https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/1921)) if you experience any trouble!
-2. Do a full install (update), but tell Ansible to stop all services (note the `stop` tag): `ansible-playbook -i inventory/hosts setup.yml --tags=setup-all,stop`
-3. Start Postgres manually by running this **on the server**: `systemctl start matrix-postgres`
-4. Run the following migration command **on the server**:
-
-```sh
-/usr/bin/env docker run --rm --name matrix-mautrix-signal-daemon \
---log-driver=none \
---user=997:1002 \
---cap-drop=ALL \
---network=matrix \
--v /matrix/mautrix-signal/signald:/signald:z \
-docker.io/signald/signald:0.20.0 \
---migrate-data
-```
-
-If you're doing this upgrade in the future, you may need to adjust the Signald version in the command above to match the up-to-date value of `matrix_mautrix_signal_daemon_version`, as seen in `roles/matrix-bridge-mautrix-signal/defaults/main.yml`. As of 2022-07-14, the signald version is `v0.20.0`
-
-5. Start all services: `ansible-playbook -i inventory/hosts setup.yml --tags=start`
-6. Tell us how this upgrade went in our [support room](README.md#support) or in [Pull Request #1921](https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/1921)
 
 
 # 2022-07-05

roles/matrix-bridge-mautrix-signal/templates/systemd/matrix-mautrix-signal-daemon.service.j2

@@ -21,6 +21,16 @@ ExecStartPre=-{{ matrix_host_command_sh }} -c '{{ matrix_host_command_docker }}
 # Intentional delay, so that the homeserver (we likely depend on) can manage to start.
 ExecStartPre={{ matrix_host_command_sleep }} 5
 
+# Migration task required by the 0.19.0 upgrade
+ExecStartPre=-{{ matrix_host_command_docker }} run --rm --name matrix-mautrix-signal-daemon \
+			--log-driver=none \
+			--user={{ matrix_user_uid }}:{{ matrix_user_gid }} \
+			--cap-drop=ALL \
+			--network={{ matrix_docker_network }} \
+			-v {{ matrix_mautrix_signal_daemon_path }}:/signald:z \
+			{{ matrix_mautrix_signal_daemon_docker_image }} \
+			--migrate-data
+
 # We can't use `--read-only` for this bridge.
 ExecStart={{ matrix_host_command_docker }} run --rm --name matrix-mautrix-signal-daemon \
 			--log-driver=none \