Provoked by https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/743

While it's kind of nice having it, it's also somewhat raw
and unnecessary.

Having a good default and not even mentioning it seems better
for most users.

People who need a more exposed bridge (rare) can use
override the default configuration using
`matrix_mautrix_signal_configuration_extension_yaml`.

We've had people who get the impression that well-known = bad,
DNS SRV = good, and who try to use DNS SRV for server delegation.

While it's true that DNS SRV can be superior for high-availability
scenarios, it's much harder to set up and comes with its own potential
downsides.

Using the well-known method is more straightforward and is enough
for almost all of us. Throwing people into the deep for no good
reason is not nice. Hopefully wording is better after this patch.

Fixed markdown error

Fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/570

Fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/641

We're getting reports of it being broken and I can confirm that the
bridge works well without it, so I don't see why we'd be asking
people to enable it.

Fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/751

Since we'll likely have generic SQLite database importing
via [pgloader](https://pgloader.io/) for migrating bridge
databases from SQLite to Postgres, we'd rather avoid
calling the "import Synapse SQLite database" command
as just `--tags=import-sqlite-db`.

Similarly, for the media store, we'd like to mention that it's
related to Synapse as well.

We'd like to be more explicit, so as to be less confusing,
especially in light of other homeserver implementations
coming in the future.

Fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/746

ma1sd requires the openid endpoints for certain functionality.
Example: 90b2b5301c/src/main/java/io/kamax/mxisd/auth/AccountManager.java (L67-L99)

If federation is disabled, we still need to expose these openid APIs on the
federation port.

Previously, we were doing similar magic for Dimension.
As per its documentation, when running unfederated, one is to enable
the openid listener as well. As per their recommendation, people
are advised to do enable it on the Client-Server API port
and use the `federationUrl` variable to override where the federation
port is (making federation requests go to the Client-Server API).

Because ma1sd always uses the federation port (unless you do some
DNS overwriting magic using its configuration -- which we'd rather not
do), it's better if we just default to putting the `openid` listener
where it belongs - on the federation port.

With this commit, we retain the "automatically enable openid APIs" thing
we've been doing for Dimension, but move it to the federation port instead.
We also now do the same thing when ma1sd is enabled.

comments in config.js must begin with two slashes

This supersedes/fixes-up this Pull Request:
https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/719

The Jitsi Web and JVB containers now (in build 5142) always
start by bulding their own default configuration
(`config.js` and `sip-communicator.properties`, respectively).

The fact that we were generating these files ourselves was no longer of use,
because our configuration was thrown away in favor of the one created
by the containers on startup.

With this commit, we're completely redoing things. We no longer
generate these configuration files. We try to pass the proper
environment variables, so that Jitsi services can generate the
configuration files themselves.

Besides that, we try to use the "custom configuration" mechanism
provided by Jitsi Web and Jitsi JVB (`custom-config.js` and
`custom-sip-communicator.properties`, respectively), so that
we and our users can inject additional configuration.

Some configuration options we had are gone now. Others are no longer
controllable via variables and need to be injected using
the `_config_extension` variables that we provide.

The validation logic that is part of the role should take care
to inform people about how to upgrade (if they're using some custom
configuration, which needs special care now). Most users should not
have to do anything special though.

Fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/735

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

Related to #681 (Github Pull Request)

Related to #681 (Github Pull Request)

Related to #681 (Github Pull Request)

This broke in 63a49bb2dc.

Proxying the OpenID Connect endpoints is now possible,
but needs to be enabled explicitly now.

Supersedes #702 (Github Pull Request).

This patch builds up on the idea from that Pull Request,
but does things in a cleaner way.

Regression since 63a49bb2dc.

Related to #685 (Github Issue).

We now automatically expose the APIs when Synapse Admin is enabled.

The SSL certificates should be accessible to the nginx proxy container, not the synapse container.

Discussed in #669 (Github Issue).