mod_restrict_xmpp: Treat archive query as a read despite using iq-set XEP-0313 uses iq-set to initiate a query, but unlike many other uses of iq-set, this does not mutate anything on the server, so it should not be treated as a write request.

This module writes out a traceback to `traceback.txt` in Prosodys data
directory (see `prosodyctl about`) when the signal `SIGUSR1` is
received. This is useful when debugging seemingly frozen instances in
case it is stuck in Lua code.