Updates default config, avoids storing muc data on prosody restart.

doc/debian/jitsi-meet-prosody/prosody.cfg.lua-jvb.example

@@ -26,6 +26,7 @@ VirtualHost "jitmeet.example.com"
         c2s_require_encryption = false
 
 Component "conference.jitmeet.example.com" "muc"
+    storage = "null"
     --modules_enabled = { "token_verification" }
 admins = { "focusUser@auth.jitmeet.example.com" }