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-synapse/tasks/synapse/setup_install.yml

@@ -65,7 +65,7 @@
     --name=matrix-config
     --user={{ matrix_user_uid }}:{{ matrix_user_gid }}
     --cap-drop=ALL
-    -v {{ matrix_synapse_config_dir_path }}:/data
+    --mount type=bind,src={{ matrix_synapse_config_dir_path }},dst=/data
     -e UID={{ matrix_user_uid }}
     -e GID={{ matrix_user_gid }}
     -e SYNAPSE_CONFIG_PATH=/data/homeserver.yaml