* Bring config.yaml.j2 in line with upstream

* Update config.yaml.j2

Most of these files were defining a service, usually toward the end.
These lines have been moved upward.

Some components (mautrix-signal, mautrix-gmessages, etc.) were defining
a service conditionally (only if metrics are exposed, etc). This was
causing issues like these in the Traefik logs:

> level=error msg="service \"matrix-mautrix-twitter\" error: port is missing" providerName=docker container=matrix-mautrix-twitter-..

This moves the comments from being just in Jinja,
to actually ending up in the generated `labels` file,
which makes inspection of the final result easier.

Also, some new lines were added here and there to make labels
more legible.

The generated file may still include weird new-lines due to
various `if` statements yielding content or not, but that's not so ugly
anymore - now that we have proper start/end sections that are visible in
the final `labels` file.

This is an attempt at optimizing service startup.

The effect is most pronounced when many services are restarted one by one.
The systemd service manager role sometimes does this - for example when `just install-service synapse` runs.
In such cases, a 5-second delay for each Synapse worker service
(or other bridge/bot service that waits on the homeserver) quickly adds up to a lot.

When services are all stopped fully and then started, the effect is not so pronounced, because
`matrix-synapse.service` starts first and pulls all worker services (defined as `Wants=` for it).
Later on, when the systemd service manager role "starts" these worker services, they're started already.
Even if they had a 5-second wait each, it would have happened in parallel.

This is backward-compatible with what we had before. We're not changing
the SSL mode - just making it configurable.

Most components are defaulting to `sslmode=disable`, while some
(`matrix-bot-matrix-reminder-bot` and others) do not specify an `sslmode` at all.

We're making sslmode configurable, because certain external Postgres
servers may be configured to require SSL encryption.
In such cases `sslmode=disable` does not work and needs to be changed to
`sslmode=require` or something else (`verify-ca`, `verify-full`, etc).

* one var to control encryption across all bridges

* move var to matrix-base

Related to https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/2427

Related to https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/2427

`metrics_enabled` should only expose the metrics locally, on the
container network, so that a local Prometheus can consume them.

Exposing them publicly should be done via a separate toggle (`metrics_proxying_enabled`).
This is how all other roles work, so this makes these mautrix roles consistent with the rest.

* Allow the mautrix whatsapp relaybot to be enable with a variable

This allows a user to enable the relaybot by setting a variable in
`vars.yml` in the same way that the mautrix signal relaybot is
configured.

* Correct default values for mautrix whatsapp relaybot variables

* Add documentation for using the relaybot with mautrix whatsapp

* Adjust variable names to better reflect what they do

* Set default variables properly and use to_json in template

We expect `--tags=start` to handle systemd reloading, so we don't need
to do it manually each time we install/uninstall a .service file.

- forego removing Docker images - it's not effective anyway, because it
  only removes the last version.. which is a drop in the bucket, usually

- do not reload systemd - it's none of our business. `--tags=start`,
  etc., handle this

- combine all uninstall tasks under a single block, which only runs if
  we detect traces (a leftover systemd .service file) of the component.
  If no such .service is detected, we skip them all. This may lead to
  incorect cleanup in rare cases, but is good enough for the most part.

This was useful when the order of these roles in relation to Synapse
mattered (when we were injecting stuff into Synapse variables during
runtime). This is no longer the case since 0ea7cb5d1812a88, so all of
this can be removed.