* Make registration proxy independent of other roles, document

Signed-off-by: Julian-Samuel Gebühr <julian-samuel@gebuehr.net>

* Fix yml issues

Signed-off-by: Julian-Samuel Gebühr <julian-samuel@gebuehr.net>

* Remove undefined variable (as service HAS to be exposed

Signed-off-by: Julian-Samuel Gebühr <julian-samuel@gebuehr.net>

* Add registration endpint

Defines the registration endpoint that should be intercepted/forwarded to the proxy

Signed-off-by: Julian-Samuel Gebühr <julian-samuel@gebuehr.net>

* Add image name

Signed-off-by: Julian-Samuel Gebühr <julian-samuel@gebuehr.net>

Signed-off-by: Julian-Samuel Gebühr <julian-samuel@gebuehr.net>

Signed-off-by: TheOneWithTheBraid <the-one@with-the-braid.cf>

Fixes: #1144

Signed-off-by: TheOneWithTheBraid <the-one@with-the-braid.cf>

Related to https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/1939

Related to https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/1108

Fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/1070

Related discussion here: 1ab507349c (commitcomment-51108407)

We'll be adding `.timer` units later on, so it's good to be
more explicit.

Fixes #586 (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.