This is split out from matrix-cactus-comments (see 241779b583),
but also heavily inspired by `matrix-static-files`.

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.

* Fix bug that prevented user with external nginx from launch

The backslash was missing and prevented users from starting the bot

* Add necessary config for ext nginx to docs

* Add automatic config for ext nginx, adjust docs

* Remove unneeded and possibly puzzeling documentation

Related to https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/1894

Related to https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/1894

Related to https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/1894

Because the configuration file is now mounted as readonly and maubot tries to update it on start,
we get this warning:
> Failed to create tempfile to write updated config to disk: [Errno 30] Read-only file system: '/config/tmpfa8vcb3y.yaml'

It doesn't seem to cause issues though.

Because the configuration is no longer overwritten on every bot start, each
next Ansible run should no longer overwrite it again and report a
"changed" task.

* Make interface hidden behind proxy by default

* Remove expose option and replace with http_bind_port

Reasoning: This is a similar binary trigger but allows to bin not on all interfaces

* Clarify maubot admin purpose

* Remove unnecessary edif

* Extend docs to prevent common misconceptions

* Make http_bind_port singular, do not allow multiple values

* Make optional again

The /data is hardcoded in the container

People often report and ask about these "failures".
More-so previously, when the `docker kill/rm` output was collected,
but it still happens now when people do `systemctl status
matrix-something` and notice that it says "FAILURE".

Suppressing to avoid further time being wasted on saying "this is
expected".

Reverts b1b4ba501fdfaa, 90c9801c560b6, a3c84f78ca9c65a, ..

I haven't really traced it (yet), but on some servers, I'm observing
`ansible-playbook ... --tags=start` completing very slowly, waiting
to stop services. I can't reproduce this on all Matrix servers I manage.
I suspect that either the systemd version is to blame or that some
specific service is not responding well to some `docker kill/rm` command.

`ExecStop` seems to work great in all cases and it's what we've been
using for a very long time, so I'm reverting to that.