This commit adds copyright headers to the same kind of docs as ones linked from e48af8a327/docs/README.md, so that these files can be reused over there.

- docs/README.md
- prerequisites.md
- configuring-dns.md
- getting-the-playbook.md
- configuring-playbook.md
- maintenance-upgrading-services.md
- maintenance-and-troubleshooting.md
- uninstalling.md

Signed-off-by: Suguru Hirahara <acioustick@noreply.codeberg.org>

Signed-off-by: Suguru Hirahara <acioustick@noreply.codeberg.org>

* Add a warning sign to "Warning" labels

Signed-off-by: Suguru Hirahara <acioustick@noreply.codeberg.org>

* Update docs/configuring-playbook-matrix-registration.md

Signed-off-by: Suguru Hirahara <acioustick@noreply.codeberg.org>

* Update docs/maintenance-and-troubleshooting.md: remove a section for ma1sd

As the project has not updated since several years, it does not seem to be reasonable to pick it up specially on the document.

Signed-off-by: Suguru Hirahara <acioustick@noreply.codeberg.org>

* Common header for sections about adjusting the playbook configuration

Signed-off-by: Suguru Hirahara <acioustick@noreply.codeberg.org>

* Update docs/configuring-playbook-dendrite.md: fix links to dendrite.yaml.j2

Signed-off-by: Suguru Hirahara <acioustick@noreply.codeberg.org>

* Update docs/configuring-playbook-bridge-mautrix-signal.md: remove a note added by a commit to remove signalgo

The note has been added with 2f6525ccb3666e0ec8f295e8eeffd78bac15a23e, apparently copied from docs/configuring-playbook-bridge-mautrix-signalgo.md

Signed-off-by: Suguru Hirahara <acioustick@noreply.codeberg.org>

* Update docs/configuring-playbook-bridge-mautrix-wsproxy.md: fix the anchor link text to mautrix-imessage documentation

Signed-off-by: Suguru Hirahara <acioustick@noreply.codeberg.org>

* Update docs/configuring-playbook-etherpad.md: add a note about the component being managed externally

Refer docs/configuring-playbook-backup-borg.md

Signed-off-by: Suguru Hirahara <acioustick@noreply.codeberg.org>

* Update docs/configuring-playbook-jitsi.md: use the common label for warning messages

Signed-off-by: Suguru Hirahara <acioustick@noreply.codeberg.org>

* Update docs/configuring-playbook-ldap-auth.md: unrecommend using ma1sd for authentication

Signed-off-by: Suguru Hirahara <acioustick@noreply.codeberg.org>

* Update docs/configuring-playbook-appservice-double-puppet.md: remove a duplicate anchor link

Signed-off-by: Suguru Hirahara <acioustick@noreply.codeberg.org>

* Update docs for old mautrix bridges for Facebook and Instagram: remove anchor links to the deleted files

Signed-off-by: Suguru Hirahara <acioustick@noreply.codeberg.org>

* Update docs/configuring-playbook-bridge-wechat.md: use common descriptions

Signed-off-by: Suguru Hirahara <acioustick@noreply.codeberg.org>

* Update docs/configuring-playbook-bridge-matrix-bridge-sms.md: create a section for the prerequisite

Signed-off-by: Suguru Hirahara <acioustick@noreply.codeberg.org>

* Update docs/maintenance-and-troubleshooting.md: use the common header text

Signed-off-by: Suguru Hirahara <acioustick@noreply.codeberg.org>

* Use common descriptions for adding the configuration

Signed-off-by: Suguru Hirahara <acioustick@noreply.codeberg.org>

* Update docs/configuring-playbook-bridge-mautrix-telegram.md: small edits

- Add a section for a Telegram API key
- Add a section for instruction about Appservice Double Puppet or Shared Secret Auth

Signed-off-by: Suguru Hirahara <acioustick@noreply.codeberg.org>

* Update docs for Draupnir and Mjolnir: replace colons with periods

Signed-off-by: Suguru Hirahara <acioustick@noreply.codeberg.org>

* Update docs/configuring-playbook-rageshake.md: adopt the common instruction

Based on docs/configuring-playbook-sygnal.md regarding the notification about necessity of the service.

Signed-off-by: Suguru Hirahara <acioustick@noreply.codeberg.org>

* Add a note about the components managed externally

Signed-off-by: Suguru Hirahara <acioustick@noreply.codeberg.org>

---------

Signed-off-by: Suguru Hirahara <acioustick@noreply.codeberg.org>
Co-authored-by: Suguru Hirahara <acioustick@noreply.codeberg.org>

Signed-off-by: Suguru Hirahara <acioustick@noreply.codeberg.org>

Fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/756

Related to https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/737

I feel like timers are somewhat more complicated and dirty (compared to
cronjobs), but they come with these benefits:

- log output goes to journald
- on newer systemd distros, you can see when the timer fired, when it
will fire, etc.
- we don't need to rely on cron (reducing our dependencies to just
systemd + Docker)

Cronjobs work well, but it's one more dependency that needs to be
installed. We were even asking people to install it manually
(in `docs/prerequisites.md`), which could have gone unnoticed.

Once in a while someone says "my SSL certificates didn't renew"
and it's likely because they forgot to install a cron daemon.

Switching to systemd timers means that installation is simpler
and more unified.

Also switches to using `docker system prune -a` for a less invasive
cleanup of Docker images and related resources.