Related to https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/1931

`|to_json` already adds the surrounding double-quotes for the string, so
adding them explicitly means we've got a double-quotes problem.

* Implement MSC 1929 Homeserver Admin Contact
Fixes #1612

For details to the proposed (not accepted yet) MSC, see:
https://github.com/matrix-org/matrix-spec-proposals/blob/hs/proposal-admin-contact-1/proposals/1929-admin-contact.md

* Implement feedback from PR #1931

* Implement feedback from PR #1931

* Fix mixed indentation

We don't have instantiated services anymore, nor
/etc/systemd/system/matrix-synapse.service.wants/ stuff.

This removes some `multi-target.wants` symlinks as well, etc.

But despite systemd saying:

> Removed symlink /etc/systemd/system/matrix-synapse.service.wants/matrix-synapse-worker@appservice:0.service

.. I still see such symlinks tehre for me for some reason, so keeping the
code (below) to find & delete them still seems like a good idea.

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.

According to the docs, "e2ee" is already under "io.element":
  https://github.com/vector-im/element-web/blob/develop/docs/e2ee.md#disabling-encryption-by-default
however "jitsi" is still under "im.vector.riot":
  https://github.com/vector-im/element-web/blob/develop/docs/jitsi.md#configuring-element-to-use-your-self-hosted-jitsi-server

For now let's just maintain backward and forward compatibility for both
settings since the client version is out of the control of this
playbook.

Related to https://github.com/vector-im/riot-web/pull/13914

Fixes #523 (Github Issue).

This will not work yet, as no version of Riot currently supports it.
It's expected to land in riot-web v1.5.16 via matrix-org/matrix-react-sdk#4348.

https://github.com/matrix-org/matrix-doc/pull/1957

Yay Riot iOS now supports integration manager discovery!

Riot used to be fine with it being blank but now it complains. This creates an ugly looking comma when there is an identity server configured but I guess that's fine.

Use Jinja2 lstrip_blocks option in templates to ensure consistent
indentation in generated files.

Use matrix_docker_network and matrix_base_data_path in matrix-remove-all
instead of hardcoded default values.

Fixes #83 (Github issue)

As suggested in #63 (Github issue), splitting the
playbook's logic into multiple roles will be beneficial for
maintainability.

This patch realizes this split. Still, some components
affect others, so the roles are not really independent of one
another. For example:
- disabling mxisd (`matrix_mxisd_enabled: false`), causes Synapse
and riot-web to reconfigure themselves with other (public)
Identity servers.

- enabling matrix-corporal (`matrix_corporal_enabled: true`) affects
how reverse-proxying (by `matrix-nginx-proxy`) is done, in order to
put matrix-corporal's gateway server in front of Synapse

We may be able to move away from such dependencies in the future,
at the expense of a more complicated manual configuration, but
it's probably not worth sacrificing the convenience we have now.

As part of this work, the way we do "start components" has been
redone now to use a loop, as suggested in #65 (Github issue).
This should make restarting faster and more reliable.