This is backward-compatible with what we had before. We're not changing
the SSL mode - just making it configurable.

Most components are defaulting to `sslmode=disable`, while some
(`matrix-bot-matrix-reminder-bot` and others) do not specify an `sslmode` at all.

We're making sslmode configurable, because certain external Postgres
servers may be configured to require SSL encryption.
In such cases `sslmode=disable` does not work and needs to be changed to
`sslmode=require` or something else (`verify-ca`, `verify-full`, etc).

* make banlist consistent
* proper multi-error message
* ignore "." MX hosts
* try recipient domain directly, even when MX records found, but failed

* live SSL certificates reload on file changes (e.g., on automatic certs renewal)
* print all errors when trying connection to an SMTP server

* fix uploads from incoming emails into matrix threads
* fix emails dequeue (account data cleanup)
* rewrite recipients handling (Cc, To, etc.)

We expect `--tags=start` to handle systemd reloading, so we don't need
to do it manually each time we install/uninstall a .service file.

- forego removing Docker images - it's not effective anyway, because it
  only removes the last version.. which is a drop in the bucket, usually

- do not reload systemd - it's none of our business. `--tags=start`,
  etc., handle this

- combine all uninstall tasks under a single block, which only runs if
  we detect traces (a leftover systemd .service file) of the component.
  If no such .service is detected, we skip them all. This may lead to
  incorect cleanup in rare cases, but is good enough for the most part.

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.