Replace some -v instances with --mount

`-v` magically creates the source destination as a directory,
if it doesn't exist already. We'd like to avoid this magic
and the potential breakage that it might cause.

We'd rather fail while Docker tries to find things to `--mount`
than have it automatically create directories and fail anyway,
while having contaminated the filesystem.

There's a lot more `-v` instances remaining to be fixed later on.
This is just some start.

Things like `matrix_synapse_container_additional_volumes` and
`matrix_nginx_proxy_container_additional_volumes` were not changed to
use `--mount`, as options for each one are passed differently
(`ro` is `ro`, but `rw` doesn't exist and `slave` is `bind-propagation=slave`).
To avoid breaking people's custom volume mounts, we keep it as it is for now.

A deficiency with `--mount` is that it lacks the `z` option (SELinux
ownership changes), and some of our `-v` instances use that. I'm not
sure how supported SELinux is for us right now, but it might be,
and breaking that would not be a good idea.

roles/matrix-client-element/templates/systemd/matrix-client-element.service.j2

@@ -21,13 +21,13 @@ ExecStart={{ matrix_host_command_docker }} run --rm --name matrix-client-element
 			-p {{ matrix_client_element_container_http_host_bind_port }}:8080 \
 			{% endif %}
 			--tmpfs=/tmp:rw,noexec,nosuid,size=10m \
-			-v {{ matrix_client_element_data_path }}/nginx.conf:/etc/nginx/nginx.conf:ro \
-			-v {{ matrix_client_element_data_path }}/config.json:/app/config.json:ro \
-			-v {{ matrix_client_element_data_path }}/config.json:/app/config.{{ matrix_server_fqn_element }}.json:ro \
+			--mount type=bind,src={{ matrix_client_element_data_path }}/nginx.conf,dst=/etc/nginx/nginx.conf,ro \
+			--mount type=bind,src={{ matrix_client_element_data_path }}/config.json,dst=/app/config.json,ro \
+			--mount type=bind,src={{ matrix_client_element_data_path }}/config.json,dst=/app/config.{{ matrix_server_fqn_element }}.json,ro \
 			{% if matrix_client_element_embedded_pages_home_path is not none %}
-			-v {{ matrix_client_element_data_path }}/home.html:/app/home.html:ro \
+			--mount type=bind,src={{ matrix_client_element_data_path }}/home.html,dst=/app/home.html,ro \
 			{% endif %}
-			-v {{ matrix_client_element_data_path }}/welcome.html:/app/welcome.html:ro \
+			--mount type=bind,src={{ matrix_client_element_data_path }}/welcome.html,dst=/app/welcome.html,ro \
 			{% for arg in matrix_client_element_container_extra_arguments %}
 			{{ arg }} \
 			{% endfor %}