Fix systemd services autostart problem with Docker 20.10

The Docker 19.04 -> 20.10 upgrade contains the following change
in `/usr/lib/systemd/system/docker.service`:

```
-BindsTo=containerd.service
-After=network-online.target firewalld.service containerd.service
+After=network-online.target firewalld.service containerd.service multi-user.target
-Requires=docker.socket
+Requires=docker.socket containerd.service
Wants=network-online.target
```

The `multi-user.target` requirement in `After` seems to be in conflict
with our `WantedBy=multi-user.target` and `After=docker.service` /
`Requires=docker.service` definitions, causing the following error on
startup for all of our systemd services:

> Job matrix-synapse.service/start deleted to break ordering cycle starting with multi-user.target/start

A workaround which appears to work is to add `DefaultDependencies=no`
to all of our services.

roles/matrix-nginx-proxy/templates/systemd/matrix-nginx-proxy.service.j2

@@ -8,6 +8,7 @@ After={{ service }}
 {% for service in matrix_nginx_proxy_systemd_wanted_services_list %}
 Wants={{ service }}
 {% endfor %}
+DefaultDependencies=no
 
 [Service]
 Type=simple