Fixes #465 (Github Issue).

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

Architecture

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

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

matrix-appservice-slack: improved documentation

Fix to avoid putting an incorrect empty jitsi.preferredDomain when no…

Discussed in #446 (Github Pull Request).

Add global var to control skype image self build

Jitsi related firewall and port changes

Fixes an error like this:

> synapse.config._base.ConfigError: Cannot reuse as_token across application services

turn tls port update

Added Jitsi firewall ports

This will not work yet, as no version of Riot currently supports it.
It's expected to land in riot-web v1.5.16 via matrix-org/matrix-react-sdk#4348.

Initial mx-puppet-skype bridge role

Hopefully fixes an error like this (which I haven't been able to
reproduce, but..):

> [modules/xmpp/strophe.util.js] <Object.i.Strophe.log>:  Strophe: Error: Failed to construct 'RTCPeerConnection': 'matrix.DOMAIN' is not one of the supported URL schemes 'stun', 'turn' or 'turns'.

These are some new defaults that we switch to, to follow upstream
changes:

- https://github.com/jitsi/docker-jitsi-meet/commit/264df04
- 3121494d4b

Jitsi security update

We define this password in the `sip-communicator.properties`
configuration file, so this is not needed for actually running JVB.

However, it does a (useless) safety check during container startup,
and we need to make that check happy.