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-dimension/templates/systemd/matrix-dimension.service.j2

@@ -23,7 +23,7 @@ ExecStart={{ matrix_host_command_docker }} run --rm --name matrix-dimension \
 			{% if matrix_dimension_container_http_host_bind_port %}
 			-p {{ matrix_dimension_container_http_host_bind_port }}:8184 \
 			{% endif %}
-			-v {{ matrix_dimension_base_path }}:/data:rw \
+			--mount type=bind,src={{ matrix_dimension_base_path }},dst=/data \
 			{% for arg in matrix_dimension_container_extra_arguments %}
 			{{ arg }} \
 			{% endfor %}