* Update docs/configuring-playbook-turn.md: add a section for description about installing

Signed-off-by: Suguru Hirahara <acioustick@noreply.codeberg.org>

* Update docs/configuring-playbook-turn.md and a related file

- Edit the introducion based on docs/configuring-playbook-client-element-web.md
- Adopt the commont format by creating the section "Adjusting the playbook configuration"
- Add the section "Extending the configuration"
- Move the section "Disabling Coturn" to the bottom

Signed-off-by: Suguru Hirahara <acioustick@noreply.codeberg.org>

* Fix capitalization: Coturn → coturn

See: https://github.com/coturn/coturn. Note that "coturn" is not capitalized even on the start of a sentence, except some rare cases like on the releases page: https://github.com/coturn/coturn/releases

Signed-off-by: Suguru Hirahara <acioustick@noreply.codeberg.org>

---------

Signed-off-by: Suguru Hirahara <acioustick@noreply.codeberg.org>
Co-authored-by: Suguru Hirahara <acioustick@noreply.codeberg.org>

Not that it seems necessary right now, but it makes it consistent with
all other roles.

.. and try to auto-switch between `bind` and `volume` depending on
whether there's a slash in the `src` path.

Fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/2482

This helps large deployments which need to open up thousands of ports
(matrix_coturn_turn_udp_min_port, matrix_coturn_turn_udp_min_port)

On a test VM, opening 1k ports takes 17 seconds for Docker to "publish"
all of these ports (setting up forwarding rules with the firewall, etc),
so service startup and shutdown take a long amount of time.

If host-networking is used, there's no need to open any ports at all
and startup/shutdown can be quick.

This paves the way for installing other roles into `roles/galaxy` using `ansible-galaxy`,
similar to how it's done in:

- https://github.com/spantaleev/gitea-docker-ansible-deploy
- https://github.com/spantaleev/nextcloud-docker-ansible-deploy

In the near future, we'll be removing a lot of the shared role code from here
and using upstream roles for it. Some of the core `matrix-*` roles have
already been extracted out into other reusable roles:

- https://github.com/devture/com.devture.ansible.role.postgres
- https://github.com/devture/com.devture.ansible.role.systemd_docker_base
- https://github.com/devture/com.devture.ansible.role.timesync
- https://github.com/devture/com.devture.ansible.role.vars_preserver
- https://github.com/devture/com.devture.ansible.role.playbook_runtime_messages
- https://github.com/devture/com.devture.ansible.role.playbook_help

We just need to migrate to those.