Add information to make jitsi work with a client in LAN

Update Jitsi docker images to stable 4416

We've had reports of the `:latest` tag not working anymore,
leading to an error as described here:
https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/341

Upgrade Synapse (1.12.3 -> 1.12.4)

Related to #454 (Github Pull Request).

Initial mx-puppet-slack bridge role

Add support for running dimension in an unfederated environment

Related to #466 (Github Pull Request).

Allow skype more configurations for relay and provisioning

Fixes #465 (Github Issue).

Related to https://github.com/xwiki-labs/synapse_scripts/pull/12.

Architecture

FIXME: horrid duplication in template file

· 😅 How to keep this in sync with the matrix-synapse documentation?
· regex location matching is expensive
· nginx syntax limit: one location only per block / statement
· thus, lots of duplicate statements in this file

· needs documentation; no checks yet for port clashes or typos in worker name
· according to https://github.com/matrix-org/synapse/wiki/Workers-setup-with-nginx#results
  about 90% of requests go to the synchrotron endpoint
· thus, the synchrotron worker is especially suited to be load-balanced
· most of the other workers are documented to support only a single instance
· https://github.com/matrix-org/synapse/blob/master/docs/workers.md

Update nginx (1.17.9 -> 1.17.10)

the changes are necessary because certbot images are tagged, so docker does not recognize the necessary architecture

This playbook now suports running dimension in both a federated and an
unfederated environment.

This config change follows:

  https://github.com/turt2live/matrix-dimension/blob/master/docs/unfederated.md

Well, actually 8cd9cde won't work, unless we put the
`|to_nice_yaml` thing on a new line.

We can, but that takes more lines and makes things look uglier.
Using `|to_json` seems good enough.

The whole file is parsed as YAML later on and merged with the
`_extension` variable before being dumped as YAML again in the end.

Expose allowed local 3pids as a configurable option

Should help with #300 (Github Issue).

Related to #451 (Github Issue).

Fix hardcoded postgres template values

Upstream set mx-puppet-skype default port to 8438