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 room account data retrieving

* show recipient's email (header `TO`)
* add `norecipient` option
* add anti-spam options (`spamcheck:` and `spamlist:`)
* fix bugs

* send emails in UTF-8 👋
* fix options descriptions
* add SMTP auth
* allow sending emails from your apps and scripts using postmoogle as email provider

.. instead of `['']`.

The final result in the `env` file will be the same (`POSTMOOGLE_ADMINS=`)
in both cases, but it's better to avoid confusion.

* postmoogle: add admins

* postmoogle: update jija2 defaults

* postmoogle: fix typo

Before this, it was trying to pull the `latest` git branch.

Related to https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/2043