Manage Jitsi configuration by ourselves for most components

We do this for 2 reasons:

- so we can control things which are not controllable using environment
variables (for example `stunServers` in jitsi/web, since we don't wish
to use the hardcoded Google STUN servers if our own Coturn is enabled)

- so playbook variable changes will properly rebuild the configuration.
When using Jitsi environment variables, the configuration is only built
once (the first time) and never rebuilt again. This is not the
consistent with the rest of the playbook and with how Ansible operates.
We're not perfect at it (yet), because we still let the Jitsi containers
generate some files on their own, but we are closer and it should be
good enough for most things.

Related to #415 (Github Pull Request).

docs/configuring-playbook-jitsi.md

@@ -34,6 +34,3 @@ Then re-run the playbook: `ansible-playbook -i inventory/hosts setup.yml --tags=
 .. and fully reload your riot-web page (at `riot.DOMAIN`).
 
 Starting a video-conference in a room with more than 2 members should then create a Jitsi widget which utilizes your self-hosted Jitsi server.
-
-
-**NOTE**: the playbook currently configures the Jitsi JVB component to use Google's STUN servers even in cases where our own [Coturn TURN server](configuring-playbook-turn.md) is enabled (it is by default). This is because JVB fails to discover its own external IP correctly when pointed to our own Coturn server. The failure happens because JVB reaches Coturn via the localnetwork and discovers a local Docker IP address instead of the public one, leading to a non-working service.