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).

roles/matrix-jitsi/defaults/main.yml

@@ -37,6 +37,9 @@ matrix_jitsi_web_transcripts_path: "{{ matrix_jitsi_web_base_path }}/transcripts
 
 matrix_jitsi_web_public_url: "https://{{ matrix_server_fqn_jitsi }}"
 
+# STUN servers used in the web UI. Feel free to point them to your own STUN server.
+matrix_jitsi_web_stun_servers: ['stun.l.google.com:19302', 'stun1.l.google.com:19302', 'stun2.l.google.com:19302']
+
 # Controls whether the matrix-jitsi-web container exposes its HTTP port (tcp/80 in the container).
 #
 # Takes an "<ip>:<port>" or "<port>" value (e.g. "127.0.0.1:12080"), or empty string to not expose.
@@ -93,7 +96,11 @@ matrix_jitsi_jvb_systemd_required_services_list: ['docker.service', 'matrix-jits
 
 matrix_jitsi_jvb_auth_user: jvb
 matrix_jitsi_jvb_auth_password: passw0rd
+
+# STUN servers used by JVB on the server-side, so it can discover its own external IP address.
+# Pointing this to a STUN server running on the same Docker network may lead to incorrect IP address discovery.
 matrix_jitsi_jvb_stun_servers: ['stun.l.google.com:19302', 'stun1.l.google.com:19302', 'stun2.l.google.com:19302']
+
 matrix_jitsi_jvb_brewery_muc: jvbbrewery
 matrix_jitsi_jvb_rtp_udp_port: 10000
 matrix_jitsi_jvb_rtp_tcp_port: 4443