This allows disabling the automatic portal bridging, meaning bridges
must be manually setup via self-servicing, by setting:

    matrix_appservice_discord_bridge_enableSelfServiceBridging: true

Signed-off-by: Ahmad Haghighi <haghighi@fedoraproject.org>

Revert "Correct inabillity for appservice-discord to connect"
This reverts commit 673e19f830.

While certain things do work even with such a local URL, sending
messages leads to an error like this:

> [DiscordBot] verbose: DiscordAPIError: Invalid Form Body
> avatar_url: Not a well formed URL.

Fixes https://github.com/Half-Shot/matrix-appservice-discord/issues/649

The sample configuration file for appservice-discord
c29cfc72f5/config/config.sample.yaml (L8)
explicitly says that we need a public URL.

Looks like there are some that I missed in 087dbe4ddc

I was thinking that it makes sense to be more specific,
and using `_postgres_` also separated these variables
from the `_database_` variables that ended up in bridge configuration.

However, @jdreichmann makes a good point
(https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/740#discussion_r542281102)
that we don't need to be so specific and can allow for other engines (like MySQL) to use these variables.

People can toggle between them now. The playbook also defaults
to using SQLite if an external Postgres server is used.

Ideally, we'd be able to create databases/users in external Postgres
servers as well, but our initialization logic (and `docker run` command,
etc.) hardcode too many things right now.

After recently updating my matrix-docker-ansible-deploy installation, matrix-appservice-discord would refuse to start, logging ECONNREFUSED to https://matrix.[mydomain]:443, which was resolving to 172.18.0.2 due to the `--hostname` in mailer grabbing that hostname.

Curious why the IRC bridge didn't have this issue, I looked into it, and it was connecting to `http://matrix-synapse:8008`.  Correcting this one to that URL resolved the issue.

This is both for consistency with 93cc71cb69976c
and for making things more obvious.

This allows for users to bridge already existing matrix rooms to discord

Discord client IDs are numeric (e.g. 12345).
Passing them as integers however, causes the Discord bridge's YAML parser
to parse them as integers and its config schema validation will fail.

Fixes #240 (Github Issue)

Fixes #230 (Github Issue).

Related to https://github.com/Half-Shot/matrix-appservice-discord/issues/510

Looks like these client ids are actually integers,
but unless we pass them as a string, the bridge would complain with
an error like:

    {"field":"data.auth.clientID","message":"is the wrong type","value":123456789012345678,"type":"string","schemaPath":["properties","auth","properties","clientID"]}

Explicitly-casting to a string should fix the problem.

The Discord bridge should probably be improved to handle both ints and
strings though.

Well, `config.yaml` has been playbook-managed for a long time.
It's now extended to match the default sample config of the Discord
bridge.

With this patch, we also make `registration.yaml` playbook-managed,
which leads us to consistency with all other bridges.

Along with that, we introduce `./config` and `./data` separation,
like we do for the other bridges.

We do use some `:latest` images by default for the following services:
- matrix-dimension
- Goofys (in the matrix-synapse role)
- matrix-bridge-appservice-irc
- matrix-bridge-appservice-discord
- matrix-bridge-mautrix-facebook
- matrix-bridge-mautrix-whatsapp

It's terribly unfortunate that those software projects don't release
anything other than `:latest`, but that's how it is for now.

Updating that software requires that users manually do `docker pull`
on the server. The playbook didn't force-repull images that it already
had.

With this patch, it starts doing so. Any image tagged `:latest` will be
force re-pulled by the playbook every time it's executed.

It should be noted that even though we ask the `docker_image` module to
force-pull, it only reports "changed" when it actually pulls something
new. This is nice, because it lets people know exactly when something
gets updated, as opposed to giving the indication that it's always
updating the images (even though it isn't).

Fixes #171 (Github Issue).