Fixed missing quotes

Use Debian Buster Docker repo on Debian Bullseye

Future maintainer: check on https://docs.docker.com/engine/install/debian/ if Docker for
Debian 11 is released, then undo this commit

Add mx-puppet-skype and mx-puppet-slack to README

I also moved matrix-sms-bridge up to match the order from container-images.md

Fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/682

Name the Synapse database on state compression import

Fixes:
https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/833

The default scalar.vector.im integrations manager doesn't support custom
URL's for etherpad, therefore Dimension needs to be enabled.

Regression since f6097fbba1

Fixes a regression introduced in f6097fbba1fb, which was cauing Synapse
to die with this error message:

> ValueError: sender_localpart needs characters which are not URL encoded.

Fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/806

These are just defensive cleanup tasks that we run.
In the good case, there's nothing to kill or remove, so they trigger an
error like this:

> Error response from daemon: Cannot kill container: something: No such container: something

and:

> Error: No such container: something

People often ask us if this is a problem, so instead of always having to
answer with "no, this is to be expected", we'd rather eliminate it now
and make logs cleaner.

In the event that:
- a container is really stuck and needs cleanup using kill/rm
- and cleanup fails, and we fail to report it because of error
suppression (`2>/dev/null`)

.. we'd still get an error when launching ("container name already in use .."),
so it shouldn't be too hard to investigate.

Correct some typos in FAQ

I don't think this was causing an issue, but it might
if the bot token has a more special value in the future.

Related to https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/828

This needs to be added for WebSocket upgrades to work properly (see doc:
http://nginx.org/en/docs/http/websocket.html)

Fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/795
and https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/822

A better fix will come later: https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/825

Fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/824

We don't have instantiated services anymore, nor
/etc/systemd/system/matrix-synapse.service.wants/ stuff.

Not specifying bind addresses for the worker resulted in this warning:

> synapse.app - 47 - WARNING - None - Failed to listen on 0.0.0.0, continuing because listening on [::]

Additionally, metrics listening only on 127.0.0.1 seems like a no-op.
Only having it accessible from within the container is likely not what
we intend. Changed that to all interfaces as well.

Whether it actually gets exposed or not depends on the systemd service
and `matrix_synapse_workers_container_host_bind_address`.

> synapse.app.generic_worker - 606 - WARNING - None - Metrics listener configured, but enable_metrics is not True!

This switches the `docker exec` method of spawning
Synapse workers inside the `matrix-synapse` container with
dedicated containers for each worker.

We also have dedicated systemd services for each worker,
so this are now:
- more consistent with everything else (we don't use systemd
instantiated services anywhere)
- we don't need the "parse systemd instance name into worker name +
port" part
- we don't need to keep track of PIDs manually
- we don't need jq (less depenendencies)
- workers dying would be restarted by systemd correctly, like any other
service
- `docker ps` shows each worker separately and we can observe resource
usage

Fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/823