Fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/2592

Part of a security hardening provoked by:
https://www.rtcsec.com/article/cve-2020-26262-bypass-of-coturns-access-control-protection/

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.

We no longer validate that there's an IP address defined.
Seems like Coturn can start without one as well, so there's no need to
require it.

If people populate `matrix_coturn_turn_external_ip_addresses` directly
to specify multiple addresses, they can leave
`matrix_coturn_turn_external_ip_address` empty.

We use the "select not equal to empty string" thing in the for loop
to avoid `matrix_coturn_turn_external_ip_address` leading to
`matrix_coturn_turn_external_ip_addresses: ['']` leading to
`external-ip=` in the Coturn configuration.

Related to https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/1741

Add support for multiple external turn IP addresses, this allows for better comptability with dualstack ipv4/ipv6 hosts, and is supported as per the documentation (point 6 here: https://matrix-org.github.io/synapse/latest/turn-howto.html#configuration)

Related to https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/999

These old versions of TLS rely on MD5 and SHA-1, both now broken, and contain other flaws. TLS 1.0 is no longer PCI-DSS compliant and the TLS working group has adopted a document to deprecate TLS 1.0 and TLS 1.1.

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

We don't provide certificates, so it fails anyway,
but we'd rather suppress the warnings about it too.

Seems like we unintentionally removed the mounting of certificates
(the `/matrix-config` mount) as part of splitting the playbook into
roles in 51312b8250.

It appears that those certificates weren't necessary for coturn to
funciton though, so we might just get rid of the configuration as well.

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.

Coturn reports it as an option that conflicts with `use-auth-secret`.
Some reasoning is here: fa523e8d09

Switching from from avhost/docker-matrix (silviof/docker-matrix)
to matrixdotorg/synapse.

The avhost/docker-matrix (silviof/docker-matrix) image used to bundle
in the coturn STUN/TURN server, so as part of the move,
we're separating this to a separately-ran service
(matrix-coturn.service, powered by instrumentisto/coturn-docker-image)