Fix etherpad binding

don't bind to any host port if nginx_proxy is used
only bind to localhost if it's not used

This leads to much easier management and potential safety
features (validation). In the future, we could try to avoid port
conflicts as well, but it didn't seem worth the effort to do it now.
Our port ranges seem large enough.

This can also pave the way for a "presets" feature
(similar to `matrix_nginx_proxy_ssl_presets`) which makes it even easier
for people to configure worker counts.

`::` leads to errors like:

> socket.gaierror: [Errno -9] Address family for hostname not supported

Add additional domains for Let's Encrypt certificates to be obtained

These validation tasks should only run when Prometheus is enabled.

Prometheus and Grafana on stats.<domain>

.. and other documentation improvements.

It seems like it doesn't cause any issues for any of these services.

We mainly switch the anonymous metrics viewing variable
to false, along with other wording changes.

The quotes around "host" for both `--pid` and `--net` were
causing trouble for me:

> docker: --pid: invalid PID mode.

and:

> docker: Error response from daemon: network "host" not found.

I've also changed the `-v` call to `--mount` for consistency with the
rest of the playbook.

Fix wrong docker image being pulled

Changed `matrix_mautrix_signal_docker_image_force_pull` to `matrix_mautrix_signal_daemon_docker_image_force_pull` when force pulling the daemon

Using the hardcoded IP did break while I was
messing with IPv6 stuff on the other branch

By running it in a more privileged container with access to the host network stack and such