add default turnserver to example image

Dockerfile.example

@@ -99,7 +99,9 @@ Pin-Priority: -1" > /etc/apt/preferences.d/firefox-nosnap && \
         adwaita-icon-theme-full \
         dbus-x11 \
         x11-apps \
-        firefox && \
+        firefox \
+        jstest-gtk \
+        coturn && \
     rm -rf /var/lib/apt/lists/* && \
     update-alternatives --set x-www-browser /usr/bin/firefox
 
@@ -147,6 +149,25 @@ RUN echo 'export DISPLAY=:0' \
     echo 'source /opt/gstreamer/gst-env' \
         >> /etc/bash.bashrc
 
+# Write turnserver script
+RUN echo "#!/bin/bash\n\
+exec turnserver\n\
+    --verbose\n\
+    --no-tls\n\
+    --listening-ip=0.0.0.0\n\
+    --listening-port=\${TURN_PORT:-3478}\n\
+    --realm=\${TURN_REALM:-example.com}\n\
+    --channel-lifetime=\${TURN_CHANNEL_LIFETIME:--1}\n\
+    --min-port=\${TURN_MIN_PORT:-49152}\n\
+    --max-port=\${TURN_MAX_PORT:-65535}\n\
+    --user selkies:selkies\n\
+    --no-cli\n\
+    --cli-password selkies\n\
+    --allow-loopback-peers\n\
+    --db \${HOME}/.config/turndb\n\
+    \${EXTRA_ARGS} \$@\n\
+" > /start-turnserver.sh && chmod +x /start-turnserver.sh
+
 # Write startup script
 RUN echo "#!/bin/bash\n\
 export DISPLAY=:0\n\
@@ -159,8 +180,14 @@ export PULSE_SERVER=unix:/run/pulse/native\n\
 sudo /usr/bin/pulseaudio -k >/dev/null 2>&1\n\
 sudo /usr/bin/pulseaudio --daemonize --system --verbose --log-target=file:/tmp/pulseaudio.log --realtime=true --disallow-exit -L 'module-native-protocol-tcp auth-ip-acl=127.0.0.0/8 port=4713 auth-anonymous=1'\n\
 [[ \${START_XFCE4:-true} == 'true' ]] && rm -rf ~/.config/xfce4 && xfce4-session &\n\
+/start-turnserver.sh &\n\
 export WEBRTC_ENCODER=\${WEBRTC_ENCODER:-x264enc}\n\
 export WEBRTC_ENABLE_RESIZE=\${WEBRTC_ENABLE_RESIZE:-true}\n\
+export TURN_HOST=\${TURN_HOST:-localhost}\n\
+export TURN_PORT=\${TURN_PORT:-3478}\n\
+export TURN_USERNAME=\${TURN_USERNAME:-selkies}\n\
+export TURN_PASSWORD=\${TURN_PASSWORD:-selkies}\n\
+export TURN_PROTOCOL=\${TURN_PROTOCOL:-tcp}\n\
 selkies-gstreamer-resize 1280x720\n\
 selkies-gstreamer\n\
 " > /entrypoint.sh && chmod +x /entrypoint.sh