* 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