feat: update Mattermost proxy configuration and documentation for improved clarity and default behavior

scripts/mattermost-proxy/run-mirror.sh

@@ -20,6 +20,9 @@ mkdir -p "$MATTERMOST_MIRROR_DIR"
 echo "Mattermost proxy mirror output: $MATTERMOST_MIRROR_DIR"
 echo "Listening on ${MATTERMOST_MIRROR_LISTEN_HOST}:${MATTERMOST_MIRROR_LISTEN_PORT}"
 echo "Launch Mattermost Desktop with: scripts/mattermost-proxy/launch-mattermost.sh"
+if [ -z "${MATTERMOST_MIRROR_HOST_ALLOW:-}" ]; then
+  echo "MATTERMOST_MIRROR_HOST_ALLOW is not set; capturing /api/v4 traffic from the proxied app."
+fi
 
 exec mitmdump \
   --listen-host "$MATTERMOST_MIRROR_LISTEN_HOST" \