Fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/1965

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.

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

Reasoning: setup_install.yml only runs on --tags=setup-all or on --tags=setup-bot-maubot.

If --tags=setup-nginx-proxy or similar commands are run, setup_install.yml will not run and the nginx configuration will be incomplete.

Co-authored-by: Slavi Pantaleev <slavi@devture.com>