restic: Fix backup container local repo mounting

If our chosen backup repo is a local one, each restic container needs to
mount the local path as a volume, otherwise the data is stuck in the
container itself.

roles/grocy/templates/docker-compose.yaml.j2

@@ -31,6 +31,9 @@ services:
         --tag grocy
       RESTIC_BACKUP_SOURCES: "/backup"
     volumes:
+{% if restic_repo is regex('^/.+') %}
+      - "{{ restic_repo }}:{{ restic_repo }}"
+{% endif %}
       - "{{ stack_grocy_env_dir }}:/backup/{{ stack_grocy_env_dir }}"
 {% endif %}