Update container definitions to run all services as a non-root user.

vars/containers/nats.yml

@@ -7,6 +7,9 @@ nats:
   # Define the docker image to be used for this container.
   image: "{{ feedstack_nats_container_image }}:{{ feedstack_nats_container_tag }}"
 
+  # Define the user that the container should be run as.
+  user: "{{ docker_user_id }}:{{ docker_group_id }}"
+
   # Define the path where application data for this container will be stored.
   appdata_directory: "{{ docker_appdata_directory }}/nats"