Restore --tags=import-synapse-sqlite-db support

Fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/2669

Removed in 04b9483f0d (2022-11-28) when switching from matrix-postgres to
the devture-postgres external Ansible role.
More details: https://github.com/spantaleev/matrix-docker-ansible-deploy/blob/master/CHANGELOG.md#matrix-postgres-has-been-replaced-by-the-comdevtureansiblerolepostgres-external-role

The `import_synapse_sqlite_db.yml` file and documentation has been adapted somewhat compared to before, so that:

- it doesn't try to start Postgres automatically. You need to handle
  this part manually
- it doesn't rely on the integrated Postgres and may potentially work
  with external Postgres instances just the same
- it doesn't wipe out the whole database anymore. By default, we assume
  it's empty anyway and there's no need for such things. If it's not,
  then it's also probably dangerous to be so destructive.

This is all completely untested, but will hopefully work.

roles/custom/matrix-synapse/tasks/import_synapse_sqlite_db.yml

@@ -0,0 +1,40 @@
+---
+
+- name: Fail if playbook called incorrectly
+  ansible.builtin.fail:
+    msg: "The `server_path_homeserver_db` variable needs to be provided to this playbook, via --extra-vars"
+  when: "server_path_homeserver_db is not defined or server_path_homeserver_db.startswith('<')"
+
+- name: Check if the provided SQLite homeserver.db file exists
+  ansible.builtin.stat:
+    path: "{{ server_path_homeserver_db }}"
+  register: result_server_path_homeserver_db_stat
+
+- name: Fail if provided SQLite homeserver.db file doesn't exist
+  ansible.builtin.fail:
+    msg: "File cannot be found on the server at {{ server_path_homeserver_db }}"
+  when: "not result_server_path_homeserver_db_stat.stat.exists"
+
+# We don't use the `docker_container` module, because using it with `cap_drop` requires
+# a very recent version, which is not available for a lot of people yet.
+#
+# Also, some old `docker_container` versions were buggy and would leave containers behind
+# on failure, which we had to work around to allow retries (by re-running the playbook).
+- name: Import SQLite database into Postgres
+  ansible.builtin.command:
+    cmd: |
+      docker run
+      --rm
+      --name=matrix-synapse-migrate
+      --log-driver=none
+      --user={{ matrix_user_uid }}:{{ matrix_user_gid }}
+      --cap-drop=ALL
+      --network={{ matrix_synapse_container_network }}
+      --entrypoint=python
+      --mount type=bind,src={{ matrix_synapse_config_dir_path }},dst=/data
+      --mount type=bind,src={{ matrix_synapse_config_dir_path }},dst=/matrix-media-store-parent/media-store
+      --mount type=bind,src={{ server_path_homeserver_db }},dst=/{{ server_path_homeserver_db | basename }}
+      {{ matrix_synapse_docker_image_final }}
+      /usr/local/bin/synapse_port_db --sqlite-database /{{ server_path_homeserver_db | basename }} --postgres-config /data/homeserver.yaml
+  register: matrix_postgres_import_synapse_sqlite_db_result
+  changed_when: matrix_postgres_import_synapse_sqlite_db_result.rc == 0

roles/custom/matrix-synapse/tasks/main.yml

@@ -45,6 +45,12 @@
     - when: matrix_synapse_enabled | bool
       ansible.builtin.include_tasks: "{{ role_path }}/tasks/import_media_store.yml"
 
+- tags:
+    - import-synapse-sqlite-db
+  block:
+    - when: matrix_synapse_enabled | bool
+      ansible.builtin.include_tasks: "{{ role_path }}/tasks/import_synapse_sqlite_db.yml"
+
 - tags:
     - register-user
   block: