* Upgrade Mjolnir from 1.1.20 to version 1.2.1

https://hub.docker.com/r/matrixdotorg/mjolnir/tags

using the "latest" tag seems inefficient as it doesn't actually redirect to the latest release

In any case, the latest release is now 1.2.1

docker pull matrixdotorg/mjolnir:v1.2.1

* Fixup

Co-authored-by: Slavi Pantaleev <slavi@devture.com>

The check was checking for an empty string in `matrix_jitsi_prosody_auth_internal_accounts`,
which is unlikely to happen. We should check for an empty list instead.

The check was not validating username/password values, so telling the user that they need a non-empty
username/password is misleading. It was merely checking if there's at least one entry in the list.

This patch adjusts the check and message accordingly.

Fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/1447

Seems like there's such a variable in the
`matrix-bridge-appservice-slack` role, which is probably where it got
copied over from.

Add a self-build option for the Dimension Dockerfile.
 - This helps further support arm64 hosts (i.e. A1.Flex w/Oracle)

Was renamed in 087dbe4ddc

It is unclear to me if there is anything you actually need to adjust with these variables. It looks like that is done automatically in `matrix_servers`.

1472958e25 reverted some of the v3 changes. I'm not sure why. Running the `workers-doc-to-yaml.sh` script now puts them back 🤷‍♂️.

https://grafana.com/blog/2021/12/07/grafana-8.3.1-8.2.7-8.1.8-and-8.0.7-released-with-high-severity-security-fix/

Related to c08880d175

We recently had someone need to inject additional configuration into
`/.well-known/matrix/client` as described here:
22b245bbd1/docs/bigbluebutton.md (have-dimension-create-meetings-with-elements-video-call-button)

There may be other use cases as well.

Fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/1393

Learn more here: https://github.com/matrix-org/synapse/releases/tag/v1.47.1

There was also a 2.1.5 security release made today.
2.2.0 contains the same security fix + more.

Both make handling of Client-Server API v3-prefixed requests better.

Related to https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/1404

We had to remove UID/GID environment variables that we used to pass
to the Synapse container, because it was causing a problem after
https://github.com/matrix-org/synapse/pull/11209

We were using both `--user` and UID/GID environment variables until now.

1f196f59cb

Related to https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/1403